A cluster headache is a type of headache that recurs over a period of time. People who have cluster headaches experience an episode marked by intense head pain one to three times per day during the cluster period, which may last from two weeks to three months. The headaches may disappear for months or years, only to recur later. Cluster headaches are one of the most severe types of headache. Follow the links below to find WebMD's comprehensive coverage about cluster headaches, what they look like, how to treat them, and much more.