Why do I get a headache after working out?

Usually a primary exercise headache - a benign pattern: throbbing pain, usually on both sides of the head, starting during or right after hard exertion, and lasting minutes to hours. Mayo Clinic splits exercise headaches into two kinds, and the split is the whole answer: primary exercise headaches are usually harmless, not connected to any underlying problem, and often preventable with medication; secondary exercise headaches come from an underlying, sometimes serious cause - bleeding or a tumor within the brain, or coronary artery disease outside it - and can require emergency care. Johns Hopkins adds the reassuring routine: a first exertion headache typically earns a brain MRI to rule out dangerous causes, and once primary is confirmed, the headaches often respond to prescription indomethacin. The lines you do not cross at home: a first-ever exercise headache, one that begins abruptly like a thunderclap, one with fever, stiff neck, vomiting, double vision, or loss of consciousness - those are same-day medical events. The common benign kind is worth mentioning to your doctor once; the scary list is not for waiting.