6. Your headache started after you hit your head. Even if it was a moderate bump and you didn't black out, you should get to the ER because your head pain may stem from a concussion. Although most such injuries are not serious, concussions with bruising or bleeding on the brain can lead to vision loss, balancing problems, confusion and even death.
7. Your head pain comes on repeatedly, in severe, sudden flashes, when you cough, sneeze, bend down, or strain during a bowel movement or sex. This may be a sign of a worrisome condition such as vascular disease of the head or neck, an aneurysm or tumor, or other structural problems in the brain.