Cluster headache (CH), also known as histamine headache, is a specific vascular headache syndrome and one of the most severe forms of headache. The underlying cause is still poorly understood but it is thought that the pain may be related to the dilation/alteration of blood vessels or to inflammation of nerves behind the eye. CH affects approximately 8-10% of all persons who suffer from headaches. They most commonly occur in men (six times more frequently than in women) between the ages of 20 and 40. They are observed more frequently among those who smoke and consume alcohol. Each headache episode generally lasts from fifteen minutes to three hours. Many such episodes may occur during a day. They tend to occur in cycles, often during the months of the year that are warmer and have more daylight. Persons who suffer from CH tend to be sociable, active and responsible and, for this reason, CH are sometimes called "the executive headache".

Only the CH victim can understand the excruciating pain and discomfort that characterize this disorder. Fortunately, only a small percentage of CH cases complain of the chronic form. Chronic CH is distinguished by its lack of a remission period lasting more than 14 days, or the absence of a remission period for more than one year.

The telltale signs of a cluster headache are distinct yet remarkably similar among CH sufferers everywhere. Here is a list of commonly reported symptoms associated with this condition:

• A piercing, stabbing pain on one side of the head and behind the eye
• Attacks occuring in clusters lasting several weeks, with a remission period of months or years between headache episodes
• Several headaches daily, recurring at the same time each day, often awakening one from sleep
• The inability to lay down or remain still
• Eye region becomes droopy, red and moist
• The nostril on the affected side becomes stuffed and runny
• There is the desire to pound one's head against a wall
• Feelings of dejection, anxiety and irritability.