Cluster headaches are severe headaches on one side of your head
that happen in groups, or "clusters." They usually occur over
weeks or months. Cluster headaches can be so painful that you
are not able to follow your normal routine or do your usual
activities. The pain is often called the worst type of headache
pain. Cluster headaches come in cycles (also called cluster
periods). Most people who get cluster headaches have one or two
cluster periods each year. A cluster period might last 1 month
or longer. After a cluster period ends, you may not get another
headache for months or even years. As you get older, it's likely
that you'll have longer and longer times without headaches. At
some point, you may not get cluster headaches ever again. Having
cluster headaches can be scary. But even though they are very
painful, cluster headaches don't cause long-term harm. During a
cycle, you may be able to reduce how often you have them, how
bad they are, and how long they last. Experts aren't sure what
causes cluster he