Most headaches are harmless, but certain features are red flags. A thunderclap headache — severe pain peaking within seconds to a minute — needs immediate emergency care because it can signal bleeding around the brain. Other warning signs include a headache with fever and a stiff neck, a headache after a recent head injury, or one accompanied by weakness, numbness, difficulty speaking, vision loss, or a seizure.
Be cautious too with a new headache after age 50, a headache that steadily worsens over days or weeks, one that is worse when lying down or wakes you at night, or new headaches in someone with cancer or a weakened immune system. Pregnant people with a new severe headache should be assessed, as it can relate to blood-pressure problems.
If any of these apply, call your local emergency number or go to urgent care. For ongoing but non-emergency headaches, a doctor can investigate the cause. Informational only, not a diagnosis.