Hypersomnia is a condition characterized by excessive daytime sleepiness or prolonged transitions to full wakefulness upon waking that is not caused by insufficient sleep. It is usually associated with mental disorders in the absence of an organic factor. To be diagnosed, the sleep disturbance must occur nearly daily for at least a month and cause significant distress or impairment. It does not include symptoms of narcolepsy like cataplexy. An organic or medical cause must be ruled out.