Lifestyle
A Sudden, Severe Headache Can Signal a Brain Aneurysm. Other Warning Signs That Call for 911
By Erica Coleman · November 1, 2026
Most headaches can be waited out. A headache that strikes suddenly and feels like the worst of a person’s life should not be.
That kind of headache is the key symptom of a ruptured brain aneurysm, according to Mayo Clinic. An aneurysm is a bulge or ballooning in a blood vessel in the brain. If it leaks or ruptures, it causes bleeding in the brain, a type of stroke.
Brain aneurysms are more common than many people realize. MedlinePlus, the National Library of Medicine’s consumer health site, says one in 50 people has a brain aneurysm, but only a small number cause symptoms or rupture. Mayo Clinic says most never rupture, and many are found only during scans done for other reasons.
When one does rupture, the National Institute of Neurological Disorders and Stroke calls it a medical emergency that can cause a stroke, brain damage, coma, and even death.
These are the warning signs listed by Mayo Clinic, NINDS and MedlinePlus.
A sudden, severe headache. NINDS says some people describe it as the worst headache of their life. MedlinePlus says it may be called a thunderclap headache.
Nausea and vomiting. All three sources list them alongside the headache.
A stiff neck. Mayo Clinic and NINDS both include it among the signs of a rupture.
Vision changes and sensitivity to light. Mayo Clinic lists blurred or double vision and sensitivity to light. MedlinePlus adds loss of vision.
Confusion, seizures or passing out. Mayo Clinic lists confusion, seizure and loss of consciousness. NINDS lists seizures and passing out for a short time or becoming unconscious.
Weakness, numbness or trouble speaking. MedlinePlus lists muscle weakness or difficulty moving any part of the body, numbness, problems speaking and a drooping eyelid.
A warning headache can come first. Mayo Clinic says an aneurysm sometimes leaks a small amount of blood days or weeks before a more severe rupture, and that a leak may cause a sudden, extremely severe headache. NINDS calls this a “warning” headache.
Some aneurysms cause trouble before they burst. A larger aneurysm that hasn’t ruptured can press on nerves and brain tissue. Mayo Clinic lists pain above and behind one eye, a dilated pupil, a change in vision or double vision, and numbness on one side of the face. NINDS also lists one pupil that is larger than the other.
What to do is simple. Mayo Clinic advises seeking medical attention right away for a sudden, extremely severe headache, and calling 911 if someone complains of one, loses consciousness or has a seizure. NINDS says to call 911 for a sudden, severe headache, especially with any other symptoms.
Several risk factors are worth knowing. Mayo Clinic says brain aneurysms are more common in women than in men, and NINDS says that risk seems to increase after menopause. Smoking and high blood pressure raise the risk that an aneurysm will form and rupture, according to Mayo Clinic, which also lists heavy alcohol use and polycystic kidney disease. MedlinePlus includes older age among its risk factors.
Family history also matters. Mayo Clinic says the risk is higher when two or more first-degree relatives, such as a parent, sibling or child, have had a brain aneurysm, and advises anyone with a family history to ask about screening.
Many aneurysms can’t be prevented, Mayo Clinic says, but quitting smoking, working with a doctor to lower high blood pressure and avoiding heavy drinking can lower the risk.
This article is for general information and is not medical advice. Call 911 for a sudden, severe headache or other signs of a stroke, and talk with your doctor about your personal risk. This article was produced with the assistance of AI and fact-checked against the sources cited by LightWave Reports.