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