Most headaches are not dangerous, but certain features point to a serious cause and need urgent assessment. A thunderclap headache, one that reaches maximum intensity within seconds to a minute, can signal bleeding around the brain and is a medical emergency. So is a headache you would describe as the worst of your life or one that feels completely different from your usual headaches.
Go to the emergency room if a headache comes with fever and a stiff neck (possible meningitis), confusion or drowsiness, seizures, weakness or numbness, difficulty speaking, vision loss, or if it follows a head injury. New headaches in people over 50, in pregnancy, in those with cancer or a weakened immune system, or headaches that steadily worsen over days also warrant prompt medical review.
Ordinary tension headaches and migraines can usually be managed at home or with advice from a pharmacist or doctor. But if you are ever uncertain, or if a headache is accompanied by any of the red flags above, seek urgent in-person care rather than waiting.