Description: For many individuals, seizures are not randomly distributed in time. They cluster. A woman may go 4 weeks with no seizures and then have three in a 30-hour period. A child may awaken and have dozens of atonic seizures with head drops over 45 minutes and then not have another seizure for the rest of the day. A cluster is usually defined by the number of seizures over a period when compared to a baseline. For some patients, however, the number of seizures may be about the same as usual, but the seizures in that period are of a different severity or type.