How do I know if a headache is serious?

Most headaches are tension-type or migraines and aren't dangerous, but certain warning signs suggest you need immediate medical attention. Seek emergency care if your headache comes on suddenly and severely like a "thunderclap," if it's the worst headache of your life, or if it's accompanied by fever, stiff neck, confusion, vision changes, weakness, numbness, or difficulty speaking. These can signal meningitis, stroke, or a brain aneurysm. Also see a doctor if headaches are progressively worsening over days or weeks, wake you from sleep, follow a head injury, or occur with persistent vomiting. Headaches that change in pattern or don't respond to usual pain relievers also warrant evaluation. When in doubt, it's always safer to get checked out.