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Clinical features

Idiopathic hypersomnia includes two distinct phenotypes, referred to as idiopathic hypersomnia with long sleep time and idiopathic hypersomnia without long sleep time.1 Idiopathic hypersomnia with long sleep time is remarkable for three symptoms: a complaint of constant or recurrent daily excessive daytime sleepiness and unwanted naps, longer and less irresistible than in narcolepsy, and nonrefreshing irrespective of their duration; night sleep is sound, uninterrupted by awakenings but abnormally prolonged; morning awakening is delayed and laborious. Patients do not awaken to the ringing of a clock or a telephone, and often rely on their spouse or a family member to wake them up. Even then, patients may remain confused, unable to react adequately to external stimuli, a state referred to as ‘sleep drunkenness’. In that sense, idiopathic hypersomnia with long sleep may be portrayed as an inability to wake up, in contrast with narcolepsy characterized by an abnormal drive to fall asleep.