A major subgroup of sleep disorders (parasomnias are the other major
subgroup) in which the predominant disturbance is in the amount, quality, or
timing of sleep. In DSM-IV, this group includes primary insomnia, primary
hypersomnia narcolepsy, breathing-related sleep disorder, and circadian rhythm
Nocturnal myoclonus is classified as a sleep disorder not otherwise
specified: it consists of repeated jerking of the limbs, particularly of the
lets, associated with brief periods of arousal.