What are cluster migraines?

Cluster migraines are severe headaches in which there may be an initial prodrome. They come in one of various cluster patterns in periods lasting at least 7 days: from one attack per day to eight per day with an average frequency of several days to over a month, usually with remissions, i.e., headache-free periods with variable duration of weeks up to more than years between the clusters lasting 1.4– 2 years.[1