A sudden “worst headache of my life” reaching its peak within an hour needs emergency assessment and consideration of head CT
Speed of onset matters. About 6% of severe headaches reaching maximum intensity within an hour in one study involved subarachnoid bleeding. Age 40 or older, neck pain/stiffness, witnessed loss of consciousness, onset during exertion, instantly peaking pain or limited forward neck movement are the rule's warning features. Most people investigated will not have bleeding, but missing it risks fatal rebleeding.
What it takes
Emergency consultation is relatively inexpensive in the Chinese estimate; head CT costs a few hundred RMB.
What you may gain
A prospective study at 10 Canadian emergency departments enrolled 2,131 people with severe headaches reaching maximum intensity within an hour; 132 (6.2%) had subarachnoid hemorrhage, bleeding around the brain. The Ottawa SAH rule uses six features: age ≥40, neck pain/stiffness, witnessed loss of consciousness, onset during exertion, thunderclap onset and limited neck flexion on examination. Any feature prompts investigation within the rule's intended population. Sensitivity was 100%, 95% CI 97.2%–100.0%, while specificity was 15.3%: it excluded only that proportion of people without bleeding.
Context & considerations
The source emphasizes how quickly pain peaks: seconds to a minute is a warning pattern, unlike a gradually worsening migraine. Vomiting, neck stiffness, light sensitivity or brief fainting add concern. Low specificity means most investigated people will have no hemorrhage, but the consequences of missed rebleeding justify evaluation. Do not simply take a painkiller and go back to sleep.
Research & references
Perry JJ, Stiell IG, Sivilotti MLA, et al. (2013). Clinical decision rules to rule out subarachnoid hemorrhage for acute headache. JAMA, 310(12), 1248-1255. https://doi.org/10.1001/jama.2013.278018