Thunderclap Headache Sydney: Causes and When to Call 000
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Thunderclap Headache — a Sudden, Severe Headache That Needs 000

A headache that reaches its full strength within about a minute needs an ambulance, every time, even if it settles. Here is why, what it can be, what the hospital does, and what comes after. Explained by a Sydney neurologist.

Headache that came on suddenly and reached its worst within a minute? Call 000 now, whether it feels severe or only moderate.

Thunderclap Headache: When It Needs 000

26 warning signs · scroll inside the boxSkip to the explainer

A thunderclap headache is less common than ordinary headaches, but it needs the same response every time, and it is an emergency until proven otherwise. The danger signs come first, so you can act before you read on. This page is written for adults. For a child with a sudden headache that reaches its worst within a minute, call 000 too.

Call 000 — or go to an emergency department — if

  • a headache comes on suddenly and reaches its worst within a minute, whether it feels severe or only moderate (including the worst headache of your life), even if it then eases, and even if you have had one before; ask for an ambulance and do not drive yourself
  • a sudden headache that reaches its worst within a minute comes on during or just after sex, hard exercise, coughing, sneezing or straining, even if you think that is the cause
  • a sudden headache comes with new neck pain or a stiff neck, or follows a neck injury, a sudden twist or stretch of the neck, or neck manipulation
  • a new headache came on suddenly, reaching its worst over a few minutes, whether it feels severe or only moderate, or is the worst of your life, or is unlike any you have had: go to an emergency department now (call 000 if you cannot get there safely)
  • the headache comes with fever and a stiff neck, a rash that does not fade when pressed, confusion or unusual drowsiness
  • you have a fever and a severe headache with vomiting, or light hurting your eyes, even without a stiff neck: go to an emergency department the same day (call 000 if you are drowsy or confused)
  • you take blood-thinning medicine or have a bleeding disorder and have a new or unusual headache, even without a head injury: go to an emergency department the same day
  • you have had a thunderclap headache checked in hospital and, since leaving, have any new or returning headache, especially in the first 3 weeks, or any new weakness, numbness, speech or vision change: go back to an emergency department the same day (call 000 if it is sudden or you have those signs)
  • a very high blood pressure reading with a headache also needs an emergency department or 000: see headache with high blood pressure
  • the headache comes with fainting, collapse or a seizure
  • the headache comes with sudden loss or dimming of vision (even if brief), double vision, a new drooping eyelid or one pupil larger than the other, slurred speech, sudden severe dizziness or unsteadiness, or numbness, weakness or drooping of the face, an arm or a leg
  • you are over 50 with a new headache, or a change in your usual headaches, and you notice blurring, double vision, or sight that dims or goes dark in one eye, even if it lasts only a few minutes
  • an eye becomes painful and red, with blurred vision, halos (coloured rings) around lights, or nausea and vomiting
  • the headache started after a head injury and is getting worse, comes with vomiting, drowsiness or confusion, or you take blood-thinning medicine
  • after a head injury, clear fluid or blood comes from your nose or an ear
  • you are 20 or more weeks pregnant or had a baby in the last 6 weeks and have a severe headache, a headache that does not get better with simple pain relief, blurred vision or flashing lights, sudden swelling of the face, hands or feet, pain under the ribs or in the upper tummy, or vomiting with a headache: go to your maternity unit or an emergency department now; a sudden headache that reaches its worst within a minute is the first item in this list, so call 000; call 000 also for a seizure, trouble breathing or chest pain
  • you have a spinal cord injury at mid-chest level or higher and get a sudden, pounding headache, often with sweating or flushing above the injury: sit upright with your legs down, loosen anything tight, check your bladder, catheter and bowel, and follow your own dysreflexia plan if you have one; call 000 if it does not settle within a few minutes or you cannot find the cause; call 000 straight away, without trying these steps first, if it is the worst headache of your life, or is unlike your usual episodes or is your first one, or comes with chest pain, weakness, a change in vision or speech, or a seizure

A sudden, explosive headache, wherever it is felt, can mean bleeding around or into the brain (a subarachnoid or intracerebral haemorrhage). It can be the only sign of a bleed, it can be moderate rather than extreme, and it can ease within minutes or hours, so how you feel afterwards cannot tell you it was nothing; about 1 in 10 to 2 in 10 people with a bleed die before they reach hospital, and treatment is urgent, which is why you ask for an ambulance rather than drive. A bleed can peak over minutes rather than seconds, so a headache that built over a few minutes goes to an emergency department now. The same sudden onset can come from a narrowing of the brain's arteries (reversible cerebral vasoconstriction syndrome, or RCVS), a tear in the wall of an artery in the neck (a dissection), which can lead to a stroke in the days after it starts, a clot in a vein of the brain, bleeding in the pituitary gland, or a leak of spinal fluid, and only tests can tell them apart. Sex, hard exercise, coughing and straining can set off an ordinary headache, but they are also the moments when these problems show themselves, so the first one is checked. A sudden headache with new neck pain, or after a neck injury or a twist of the neck, can mean a dissection. Fever with a stiff neck, or a rash that does not fade when pressed, can mean meningitis; fever with a severe headache and vomiting, or light hurting the eyes, can too, even when the neck is not stiff. Blood-thinning medicine or a bleeding disorder makes bleeding inside the skull more likely, even after a minor knock or none. A very high blood pressure reading with a headache can mean a dangerous surge in pressure. After a thunderclap has been checked, a returning severe headache can mean a related problem, such as a narrowed artery, that needs another look, and a stroke can follow a few days after a first normal scan. A seizure, fainting or collapse with a headache needs urgent checks for a cause in the brain. Weakness, numbness or drooping of the face, trouble speaking, sudden unsteadiness or a sudden loss of vision can mean a stroke. Double vision, a new drooping eyelid or a change in the size of one pupil can mean pressure on a nerve from a bulging blood vessel (an aneurysm) or a dissection. In someone over 50, a new headache with a change in vision can mean giant cell arteritis is cutting off the blood supply to the eye: treated the same day, sight can usually be saved, but sight that is lost rarely comes back. A painful red eye with blurred vision and halos can mean a sudden rise in the pressure inside the eye (acute angle-closure glaucoma), which can permanently damage sight if it is not treated quickly. After a head injury, bleeding inside the skull can build up over hours, sometimes after a spell of feeling well, and clear fluid or blood from the nose or an ear is a sign of a severe head injury. In pregnancy or after a birth, a severe headache can be the first sign of pre-eclampsia, a condition of high blood pressure in pregnancy that can lead to seizures, and RCVS is more likely around a birth, so a severe headache goes to the maternity unit or an emergency department now, and a sudden one that peaks within a minute goes to 000. After a spinal cord injury, a pounding headache can be autonomic dysreflexia, a sudden surge in blood pressure set off by something below the injury, such as a full bladder; it needs urgent treatment. If you have migraine, your usual aura (shimmering or zigzag lines that spread slowly over several minutes and clear within an hour) does not need 000 on its own, and nor do the eye signs of your usual attack of a cluster headache that a doctor has already diagnosed, as your doctor described it (a red, watering eye, a drooping eyelid or a smaller pupil). A first cluster-like attack, a first aura after 50, or an attack or aura that is different from your usual ones needs an emergency department the same day; call 000 if it comes with a new drooping eyelid, one pupil larger than the other, or a headache that reached its worst within a minute. If a doctor has diagnosed a headache brought on by sex, exercise or coughing after tests, your usual attack, the same as the ones you were told to expect, does not need 000 on its own; the first attack, one that is different, much worse or longer than usual, or one with fainting, vomiting, confusion, drowsiness, weakness, numbness or a change in vision, does. A brief stab of pain that is over within seconds and leaves no headache behind is a different pattern (see ice pick headache); a sudden headache that lasts is not, and belongs in the first item of this list. If a stab is new, severe or keeps repeating, see your GP; if any headache remains afterwards, treat it as the first item. Remember FAST: Face drooping, Arm weakness, Speech difficulty, Time to call 000.

See your GP the same day if

  • a new headache built over hours, is less severe and is unlike your usual headaches (if it was severe or reached its worst over a few minutes, see the list above; if you are not sure whether it reached its worst within a minute, treat it as the first item in the 000 list)
  • a headache brought on by sex, hard exercise, coughing, sneezing, laughing or straining was not sudden, and it is the first time: see your GP the same day and ask for it to be checked as a first one (if it was sudden, see the list above)
  • it is a new headache, or a change in your usual headaches, and you are over 50, especially with a new tender scalp that does not go away, pain in the jaw when you chew that eases when you stop, aching shoulders, or feeling generally unwell; with any change in your vision, see the list above
  • the headache is getting steadily worse over days or weeks
  • the headache is worse when you lie down, or is worst on waking and comes with vomiting or blurred vision
  • the headache is brought on by coughing, sneezing, laughing or straining, was not sudden, and is not the first time you have had one (if it was sudden, see the list above)
  • you have a fever with the headache
  • it is a new headache, or a change in your usual headaches, and you have, or have had, cancer, or you have a weakened immune system
  • you are pregnant or have had a baby in the last 6 weeks and have a headache: contact your midwife, maternity unit or GP the same day; with blurred vision or sudden swelling of the face, hands or feet, contact your maternity unit or go to hospital now

A headache that built over hours and is milder can still be the start of something serious, and a person cannot always tell the patterns apart, so a new one that is unlike your usual headaches is checked the same day, and the 000 list wins whenever there is doubt. A first headache brought on by sex or exertion, even if it was not sudden, is the one that classification says must be checked for a bleed, a torn artery and RCVS. In someone over 50, a new tender scalp that does not go away, or jaw pain on chewing, can mean giant cell arteritis, an inflammation of the arteries of the head that can threaten sight, so it is checked that day. A headache that is getting steadily worse, or worse when you lie down, or worst on waking with vomiting or blurred vision, can mean raised pressure inside the head. A headache brought on by coughing or straining can come from a problem at the back of the brain, so it is checked if a doctor has not already looked into it. Fever can mean an infection. Cancer, a weakened immune system, and pregnancy or a recent birth each make some serious causes more likely, so the bar for checking is lower. If you cannot see your GP that day, go to an emergency department. If something matches both lists, follow the 000 list.

Where most people sit

Most people who go to an emergency department with a thunderclap headache turn out not to have a bleed: in a study of 644 adults, a subarachnoid haemorrhage was found in about 1 in 28, and a serious cause of any kind in about 1 in 9. But nobody can tell which person they are from how the headache feels, and checking is what finds the ones who need treatment. That is why the advice is the same every time.

What Is a Thunderclap Headache?

It arrives like a clap of thunder. One moment you are fine; the next you have a severe headache at full strength, often described as the worst of your life or as an explosion in the head. Neurologists define it by its speed: the classification of headache disorders, the rulebook they use, describes pain that reaches its maximum in less than a minute and lasts at least five minutes. In practice, you do not need a stopwatch. If the pain went from nothing to its worst almost at once, treat it as a thunderclap and call 000.

Why the rush? Because a thunderclap headache is a warning sign, not a diagnosis. The classification says that it is frequently associated with serious vascular conditions inside the head, and that doctors must exclude them. The most common causes are bleeding around the brain (a subarachnoid haemorrhage) and a narrowing of the brain's arteries (RCVS). A bleed can be the only sign: the pain may be moderate, and you may feel well within the hour. Misdiagnosis is common, most often as migraine, in one quarter to one half of people with a bleed, and delay can be catastrophic. So the question is not "how bad was it?" but "how fast did it come on?".

Thunderclap headache is less common than ordinary headaches, but it needs the same response every time. In a study across emergency departments, 14 in every 100 people who came in with a main complaint of headache described a thunderclap onset. Most of them turned out not to have a bleed. But the people who did were found only because everyone was checked.

Where most people sit

Most headaches, including most severe ones, come on over minutes to hours and are migraine or tension-type headache. A true thunderclap, full strength within a minute, is the exception. That speed, a peak within a few minutes, severe or only moderate, or a headache unlike any you have had are the features that change the advice to calling 000 or going to an emergency department now.

What Can Cause a Thunderclap Headache?

A thunderclap headache can be the first sign of several different conditions. The table lists the main ones. You cannot work out which you have from the symptoms alone, and several can look the same on the first scan, which is why hospital doctors look for all of them.

Swipe the table sideways to see all three columns →

CauseWhat it isWhat to know
Subarachnoid haemorrhageBleeding into the fluid-filled space around the brain, often from a bulge in a blood vessel (an aneurysm)The most feared cause. It can be the only symptom, and the headache can be moderate. A neurosurgical emergency.
Reversible cerebral vasoconstriction syndrome (RCVS)The arteries of the brain narrow in places, then recover, usually within about 3 monthsThunderclaps that repeat over days. More than half of cases follow a birth or some medicines and drugs; it also occurs without either. Can lead to stroke or bleeding, sometimes a few days after a first normal scan.
Artery dissectionA tear in the wall of an artery in the neck or headMay come with neck, face or head pain on one side, sometimes after a neck injury or twist. Can lead to a stroke in the days after it starts.
Clot in a vein of the brainA blood clot in the veins that drain the brain (cerebral venous thrombosis)No typical pattern: the headache can be sudden, can build over time, or can be mild.
Pituitary apoplexyBleeding in, or loss of blood supply to, the pituitary gland at the base of the brainEasy to miss.
Spinal fluid leakLow pressure of the fluid around the brain (spontaneous intracranial hypotension)Usually worse upright and better lying down, but it can start suddenly. See headache when standing up.
Other causesBleeding inside the brain, stroke, meningitis, a cyst blocking the flow of fluid, a sudden surge in blood pressure, a sinus infection with a change in pressureAll can start with a sudden headache and need emergency care.
Primary thunderclap headacheA thunderclap headache with no cause foundA diagnosis of last resort, made only when every cause has been shown to be absent.
  • Primary thunderclap headache. The classification calls this a diagnosis of last resort, reached only when all organic causes have been demonstrably excluded, and notes that the evidence that it exists as a primary disorder is poor. Some reviewers think such cases may be missed causes. It is never a diagnosis to make at home.
  • Headaches brought on by sex, exercise or coughing. These can be primary headaches with no dangerous cause, but each can also present as a thunderclap, and on the first occurrence a doctor must exclude a bleed, a torn artery and RCVS. See the section after the emergency, below, and headache after exercise.
  • Migraine and cluster headache. Both can be severe and fast, but they build over minutes to hours and come in attacks. Neither is a reason to skip 000 when a headache reaches its worst within a minute. Read our migraine overview and cluster headache pages.
  • Ice pick headache. A stab over in seconds, with no headache left behind. See ice pick headache.

What Happens in Hospital?

The emergency team asks how the headache started and how fast, examines you, and usually arranges a CT scan of the brain. Which tests follow depends on your story and on how many hours have passed. They can include:

  • A CT scan of the brain. It is quick and shows blood. It is most reliable early: in a Canadian study of alert adults scanned within six hours and read by qualified radiologists, CT found every one of 121 bleeds, while across all 3,132 people scanned it found 92.9%. Its ability to find a bleed is highest in the first hours and, in most studies, falls as time passes; some newer studies find modern scanners stay sensitive for a day or two, but doctors still decide case by case whether more tests are needed.
  • A lumbar puncture. A needle in the lower back takes a sample of the fluid around the brain, which can show blood that a scan has missed. It is often used when the scan is clear but a bleed is still possible.
  • A scan of the blood vessels of the head and neck. It looks for a bulge (an aneurysm), a narrowing (RCVS) or a tear (a dissection).
  • An MRI scan. It is used when the earlier tests do not give an answer, and can show a clot in a vein or a change in the pituitary gland.

A review in a neurology journal puts the sequence this way: a brain CT scan, then a lumbar puncture if the scan does not give the diagnosis, then an MRI and imaging of the vessels of the head and neck if there is still no answer. Doctors may also use a checklist such as the Ottawa subarachnoid haemorrhage rule. It was tested on alert adults with a normal examination whose headache peaked within an hour; in that group it missed no bleeds. It is a tool for emergency doctors, not for use at home, and it does not replace an assessment.

A normal scan does not always settle it

A scan is a snapshot. It is most sensitive in the first hours, and some causes, such as a narrowed artery, a torn artery or a clot in a vein, may not show on a first CT scan at all. In RCVS the narrowing is at its maximum on scans 2 to 3 weeks after the headache starts, and a stroke can follow a few days after a first normal scan. So a thunderclap headache can need more than one test, or a repeat, and "the scan was normal" is the start of the follow-up, not the end of it. If a new sudden, severe headache comes on later, call 000 again.

After the Emergency: What Follow-Up Looks Like

What happens next depends on what the hospital found. If a cause is found, the hospital team treats it. If everything is normal, you may be told the headache was a primary one, a diagnosis made only after the search. Either way, ask the team before you leave:

  • what was found, which tests were done, and when
  • whether a repeat scan or an appointment is planned, and with whom
  • what to do if it happens again (the answer is 000 again, unless your treating team has given you a different written plan)
  • when you can go back to exercise, work, travel and sex

Your GP is the usual next step. Headaches brought on by sex, exercise or coughing, once a doctor has checked the first, can be primary headaches. For sex, the classification describes a headache that builds with excitement or turns explosive at orgasm and lasts from a minute to a day; some people have one attack in a lifetime, and in up to 4 in 10 the headache runs a chronic course for more than a year. If you have been given that diagnosis, ask your doctor what to expect and what would count as different.

A new thunderclap is never a booking: call 000

If another sudden headache that reaches its worst within a minute comes after your checks, call 000. Do not book an appointment, do not wait to see your GP, and do not decide it is the same as last time. Booking a consultation is for the weeks after an emergency, not a substitute for 000.

When to See a Neurologist After a Thunderclap Headache

  • You have been through emergency checks, no cause was found, and you want a clear explanation and plan
  • You have headaches brought on by sex, exercise or coughing and want to understand the pattern
  • You have had a narrowing of the brain's arteries (RCVS) or another cause treated in hospital and want follow-up
  • Your headaches have continued or changed since hospital, and your GP has seen you
  • You have been told your scans are normal, but you remain worried

A consultation involves a detailed history, a neurological examination and a plan, coordinated with your GP and the hospital team. It is for follow-up and planning, never for a new sudden, severe headache: that is 000. Dr Ron Granot trained at Prince of Wales Hospital, Sydney, and sees patients in Bondi Junction. Ask your GP for a referral. For the wider picture, read our migraine overview and the headache diary tool.

Frequently Asked Questions

What is a thunderclap headache? +
A thunderclap headache is a very severe headache that reaches its full strength within about a minute, like a clap of thunder. The classification of headache disorders describes pain that reaches its maximum in less than 1 minute and lasts at least 5 minutes, but do not wait to see how long it lasts. It is a warning sign rather than a diagnosis: it can be the first sign of bleeding around the brain (a subarachnoid haemorrhage), a narrowing of the brain's arteries (reversible cerebral vasoconstriction syndrome, or RCVS), a tear in the wall of an artery in the neck (a dissection), a clot in a vein of the brain, bleeding in the pituitary gland, or a leak of spinal fluid. The pain does not have to be extreme: bleeding around the brain can cause a headache that is moderate and has no other signs. Call 000 for any headache that comes on suddenly and reaches its worst within a minute, whether it feels severe or only moderate, even if it then eases and even if you have had one before, and ask for an ambulance. Also call 000 for a headache with fever and a stiff neck, a rash that does not fade when pressed, confusion, fainting, collapse or a seizure, or with weakness, numbness or drooping of the face, an arm or a leg, trouble speaking, a loss of vision or double vision. If you are 20 or more weeks pregnant or had a baby in the last 6 weeks, a severe headache needs your maternity unit or an emergency department now, and a sudden one that reaches its worst within a minute needs 000. A new headache that came on suddenly and reached its worst over a few minutes, or is the worst of your life, needs an emergency department now.
Can a thunderclap headache turn out to be nothing serious? +
Only emergency checks can tell, never you at home. Sometimes it does turn out to be nothing serious. In a study of 644 adults who came to emergency departments with a thunderclap headache, a serious cause was found in about 1 in 9 (10.9 in 100) and a subarachnoid haemorrhage, a bleed around the brain, in about 1 in 28 (3.6 in 100); most had a benign cause. Doctors call a thunderclap headache primary, meaning no cause found, only as a last resort after every cause has been shown to be absent, and the classification says the search should be expedited and exhaustive. The checking is what finds the people who do have a bleed, and a bleed can be missed at first: the first diagnosis is wrong in one quarter to one half of people with one, most often called migraine. So feeling well afterwards cannot stand in for the checks. Call 000 for any headache that comes on suddenly and reaches its worst within a minute, whether it feels severe or only moderate, even if it then eases and even if you have had one before, and ask for an ambulance. Also call 000 for a headache with fever and a stiff neck, a rash that does not fade when pressed, confusion, fainting, collapse or a seizure, or with weakness, numbness or drooping of the face, an arm or a leg, trouble speaking, a loss of vision or double vision. If you are 20 or more weeks pregnant or had a baby in the last 6 weeks, a severe headache needs your maternity unit or an emergency department now, and a sudden one that reaches its worst within a minute needs 000. A new headache that came on suddenly and reached its worst over a few minutes, or is the worst of your life, needs an emergency department now.
What does a thunderclap headache feel like? +
People describe a sudden, explosive pain that peaks within seconds to a minute, often the worst headache of their life. It can be felt anywhere in the head or at the back of the head and neck, and it can come with nausea, vomiting, neck pain or stiffness, or a brief faint. Speed is the clue, not the place or the score out of 10: bleeding around the brain can cause a headache that is moderate and has no other signs. A new headache that came on suddenly, reaching its worst over a few minutes, whether it feels severe or only moderate, or that is the worst of your life or unlike any you have had, needs an emergency department now (call 000 if you cannot get there safely). A new headache that built over hours, is less severe and is unlike your usual ones needs your GP the same day. If you are not sure whether it reached its worst within a minute, treat it as a thunderclap and call 000. Call 000 for any headache that comes on suddenly and reaches its worst within a minute, whether it feels severe or only moderate, even if it then eases and even if you have had one before, and ask for an ambulance. Also call 000 for a headache with fever and a stiff neck, a rash that does not fade when pressed, confusion, fainting, collapse or a seizure, or with weakness, numbness or drooping of the face, an arm or a leg, trouble speaking, a loss of vision or double vision. If you are 20 or more weeks pregnant or had a baby in the last 6 weeks, a severe headache needs your maternity unit or an emergency department now, and a sudden one that reaches its worst within a minute needs 000. A new headache that came on suddenly and reached its worst over a few minutes, or is the worst of your life, needs an emergency department now.
Can stress cause a thunderclap headache? +
Stress can bring on ordinary headaches, but a sudden headache is not put down to stress until the emergency causes have been looked for: the classification calls a thunderclap headache with no cause found a diagnosis of last resort. Straining, coughing, hard exercise and sex can set off a thunderclap headache, and they are also the moments when a bleed or a problem with an artery can show itself, so the first one is checked in hospital. Once the checks are done, a doctor can tell you whether stress or anything else plays a part in the headaches that follow. Call 000 for any headache that comes on suddenly and reaches its worst within a minute, whether it feels severe or only moderate, even if it then eases and even if you have had one before, and ask for an ambulance. Also call 000 for a headache with fever and a stiff neck, a rash that does not fade when pressed, confusion, fainting, collapse or a seizure, or with weakness, numbness or drooping of the face, an arm or a leg, trouble speaking, a loss of vision or double vision. If you are 20 or more weeks pregnant or had a baby in the last 6 weeks, a severe headache needs your maternity unit or an emergency department now, and a sudden one that reaches its worst within a minute needs 000. A new headache that came on suddenly and reached its worst over a few minutes, or is the worst of your life, needs an emergency department now.
Thunderclap headache during sex or exercise: is it serious? +
If it was sudden, call 000 the first time, and any time it is sudden unless a doctor has diagnosed a primary headache after tests (see below). A first headache with sex or exercise that was not sudden still needs your GP the same day, to be checked as a first one. The classification says that on the first onset of headache with sexual activity it is mandatory to exclude a subarachnoid haemorrhage, a tear in an artery and RCVS, and it says the same for the first headache brought on by exercise. If tests find no cause, a doctor may diagnose a primary headache of sex or exercise: sex headache builds with excitement or turns explosive at orgasm, lasts from 1 minute to up to a day when severe, and comes only with the trigger. Some people have just one in a lifetime, and in up to 4 in 10 the headaches run a chronic course for more than a year. If a doctor has diagnosed this after tests, your usual attack, the same as the ones you were told to expect, does not need 000 on its own; the first attack, one that is different, much worse or longer than usual, or one with fainting, vomiting, confusion, drowsiness, weakness, numbness or a change in vision, does. A headache after sex that is worse when upright and better lying down can be a spinal fluid leak: see your GP the same day, and call 000 if it came on suddenly and reached its worst within a minute. Call 000 for any headache that comes on suddenly and reaches its worst within a minute, whether it feels severe or only moderate, even if it then eases and even if you have had one before, and ask for an ambulance. Also call 000 for a headache with fever and a stiff neck, a rash that does not fade when pressed, confusion, fainting, collapse or a seizure, or with weakness, numbness or drooping of the face, an arm or a leg, trouble speaking, a loss of vision or double vision. If you are 20 or more weeks pregnant or had a baby in the last 6 weeks, a severe headache needs your maternity unit or an emergency department now, and a sudden one that reaches its worst within a minute needs 000. A new headache that came on suddenly and reached its worst over a few minutes, or is the worst of your life, needs an emergency department now.
If a thunderclap headache goes away, do I still need to go to hospital? +
Yes. Call 000 whether or not it settles. A headache that eases does not rule out a bleed or a tear in an artery, and a bleed can cause a headache that is moderate and has no other signs. Speed helps: a CT scan is most sensitive in the first hours, and in a Canadian study of alert adults scanned within six hours and read by qualified radiologists, it found all 121 bleeds among 953 people, while across all 3,132 people it found 92.9%. Do not drive yourself; ask for an ambulance. A normal scan, especially a later one, does not always settle it, which is why hospital doctors choose the tests, and may add or repeat them. Do not wait for it to come back before you act. Call 000 for any headache that comes on suddenly and reaches its worst within a minute, whether it feels severe or only moderate, even if it then eases and even if you have had one before, and ask for an ambulance. Also call 000 for a headache with fever and a stiff neck, a rash that does not fade when pressed, confusion, fainting, collapse or a seizure, or with weakness, numbness or drooping of the face, an arm or a leg, trouble speaking, a loss of vision or double vision. If you are 20 or more weeks pregnant or had a baby in the last 6 weeks, a severe headache needs your maternity unit or an emergency department now, and a sudden one that reaches its worst within a minute needs 000. A new headache that came on suddenly and reached its worst over a few minutes, or is the worst of your life, needs an emergency department now.
What tests will the hospital do for a thunderclap headache? +
The emergency team takes your history, examines you and usually arranges a CT scan of the brain. If it does not give the answer and a bleed is still possible, they may do a lumbar puncture (a needle in the lower back that takes a sample of the fluid around the brain) or a scan of the blood vessels of the head and neck, and sometimes an MRI scan. Which tests, and when, depends on your story and on the time since the headache began. A CT scan is most reliable early, and a narrowed artery, a torn artery or a clot in a vein may not show on a first scan: in RCVS the narrowing is at its maximum on scans 2 to 3 weeks after the headache starts, and a stroke can follow a few days after a first normal scan. Doctors may also use a checklist such as the Ottawa subarachnoid haemorrhage rule, which was tested on alert adults with a normal examination whose headache peaked within an hour; it is a tool for emergency doctors, not for use at home. Ask the hospital team who will follow you up and what to do if it happens again. Call 000 for any headache that comes on suddenly and reaches its worst within a minute, whether it feels severe or only moderate, even if it then eases and even if you have had one before, and ask for an ambulance. Also call 000 for a headache with fever and a stiff neck, a rash that does not fade when pressed, confusion, fainting, collapse or a seizure, or with weakness, numbness or drooping of the face, an arm or a leg, trouble speaking, a loss of vision or double vision. If you are 20 or more weeks pregnant or had a baby in the last 6 weeks, a severe headache needs your maternity unit or an emergency department now, and a sudden one that reaches its worst within a minute needs 000. A new headache that came on suddenly and reached its worst over a few minutes, or is the worst of your life, needs an emergency department now.

Related: Migraine overview · Migraine aura · Headache with nausea · Headache after exercise · Headache when standing up · Cervicogenic headache · Headache at the back of the head · Headache on top of the head · Headache with high blood pressure · Tension headache · Headache on the left side · Headache in the temples · Sinus headache · Cluster headache · Ice pick headache · Trigeminal neuralgia · Medication overuse headache · Headache diary tool · For GPs

Important: This page is general health information for adults living in Australia and is not a substitute for individual medical advice. If you have a sudden headache that reaches its worst within a minute, whether it feels severe or only moderate, even if it eases, a sudden headache during sex, hard exercise, coughing or straining, a sudden headache with new neck pain or after a neck injury, a very high blood pressure reading with a headache, a headache with a stiff neck and fever, confusion, a rash that does not fade when pressed, fainting, collapse or a seizure, a headache with weakness, numbness or drooping of the face, an arm or a leg, sudden loss of vision, double vision, slurred speech or sudden unsteadiness, a painful red eye with blurred vision, a headache that is getting worse or comes with vomiting after a head injury, clear fluid or blood from the nose or an ear after a head injury, or, if you are over 50, a new headache with blurring, double vision or dimming of sight, or any other warning sign listed at the top of this page, call 000 or go to an emergency department. If you are 20 or more weeks pregnant or had a baby in the last 6 weeks and have a severe headache, vomiting with a headache, blurred vision or flashing lights, go to your maternity unit or an emergency department now; a sudden headache that reaches its worst within a minute needs 000. Diagnosis and treatment decisions are made on an individual basis with your treating doctor.
Sources: the studies and guidelines behind this page
  • The international classification of headache disorders (sections 4.2, 4.3, 4.4, 6.2.2 and 6.6.1): Headache Classification Committee of the International Headache Society. Cephalalgia 2018;38:1-211. PubMed 29368949
  • Causes and assessment: Schwedt TJ, Matharu MS, Dodick DW. Lancet Neurol 2006;5:621-31 (PubMed 16781992); Schwedt TJ. Continuum 2015;21:1058-71 (PubMed 26252591); Ducros A. Lancet Neurol 2012;11:906-17 (RCVS; PubMed 22995694); Equiza J, et al. Pract Neurol 2020 (pituitary apoplexy; PubMed 33060192); Bahra A. J Neurol 2020;267:1554-66 (PubMed 32130497).
  • How often it is serious, and the scan: Roberts T, et al. Emerg Med J 2022;39:803-809 (the study of 644 people; PubMed 35144978); Perry JJ, et al. BMJ 2011;343:d4277 (PubMed 21768192); Vincent A, et al. Emerg Med J 2022;39:810-817 (PubMed 34819306); Perry JJ, et al. JAMA 2013;310:1248-55 (the Ottawa rule; PubMed 24065011); Perry JJ, et al. CMAJ 2017;189:E1379-E1385 (PubMed 29133539).
  • Guidance: healthdirect, Headaches (last reviewed May 2025); NHS, Subarachnoid haemorrhage (reviewed September 2025); the sibling pages on this site for the pregnancy, spinal cord injury, head injury and over-50 items.

This number is not an emergency line. For a sudden headache, call 000.

After the Emergency: Follow-Up With Dr Granot

Book a consultation with Dr Ron Granot — neurologist with a special interest in headache, Bondi Junction. Ask your GP for a referral, then get in touch.

Book a Consultation
Call Us02 9388 0615
LocationSuite 301, Bondi Junction
Emailreception@eastneurology.com.au

Last reviewed: 7 November 2026 by Dr Ron Granot, FRACP — Consultant Neurologist, East Neurology, Bondi Junction.

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