A cluster headache is similar to a migraine, in that it causes severe pain on one side of the head. However, cluster headaches last only 15 minutes to 2 hours, while migraines can run for hours or even days. In addition, cluster headaches can recur as many as eight times in a single day. These headaches occur primarily in men, especially those between the ages of 20 and 40. Cluster headaches are so-named because they tend to appear in groups or clusters. The pain may strike several times a day for several weeks and then disappear for several years. They typically occur in the night or early morning, and may recur about the same time each day. Cluster headaches start as a sudden, sharp pain behind one eye and progress to a steady, severe pain. The headache causes the affected eye to become red and water profusely, and the nostril on that side to become congested and runny. The pupil on the affected side may be smaller, and the eyelid may puff up or droop. During a cluster period, headaches may be triggered by drinking alcohol. Most victims are smokers, though quitting smoking doesn't usually stop the headaches. Several prescription medications can reduce the headache symptoms, or even prevent them. If you think you may be suffering from cluster headaches, talk to a health care provider.