Headaches are extremely common—almost everyone will experience at least one tension headache in their lives—but they usually go away without causing further problems. However, if you experience any of the situations below, you should see a doctor or go to the emergency room.

"Thunderclap" Headache

This is an extremely severe headache—one you'd describe as the worst of your life—that comes on very rapidly in the space of 60 seconds or less. Bleeding in the brain, caused by an aneurysm or other injury, and stroke can both cause thunderclap headaches.

Following a Head Injury

Any head trauma that causes a headache requires prompt medical attention. A headache after any kind of impact to the head, even a minor fall or bump, can indicate concussion, especially if the headache continues to worsen after the injury. Even what may seem like minor trauma to the head can result in bleeding in the brain that can be life-threatening.

Fever or Stiff Neck

A headache combined with a fever or stiff neck can indicate encephalitis (infection of the brain) or meningitis (infection of the membrane surrounding the brain), both of which are life-threatening.

Headache that Wakes You Up

This is a common symptom of cluster headaches, which are not life-threatening but can be debilitating.

Nausea, Vomiting, or Sensitivity to Light/Sound

This is a common symptom of migraine headaches, which can keep patients away from work or other normal activities.