What is cluster headache?

Cluster headache are attacks of severe, one-sided pain, usually in or around the eye that last for 15-180 minutes. Attacks can occur from once every other day up to eight times per day, and the attacks happen in groupings or “clusters” that last for weeks or months. Between clusters, symptom-free periods last months to years. During the worst attacks, the intensity of pain is excruciating. 

Cluster headache pain is also associated with at least one of the following: eye redness or watering on the same side of the pain, congested or runny nostril on the same side of the pain, swollen eyelid on the same side of the pain, facial/forehead sweating on the same side of the pain, smaller pupil or drooping eyelid on the same side of the pain, or a sense of restlessness or agitation. Cluster headache is a rare headache disorder compared to migraine. For unknown reasons, men are affected more often than women.