The diagnosis is difficult, as more common causes of sleepiness, including sleep deprivation, use of drugs or substances, psychiatric or medical disorders and genuine sleep disorders (sleep disordered breathing, narcolepsy, periodic leg movement disorders) should be first ruled out. Since it has been distinguished from narcolepsy,1 idiopathic hypersomnia has been defined according to small cases series, with various clinical forms. The alertness is continuously decreased during daytime, possibly culminating in irresistible needs for sleeping. Naps are either refreshing or, more typically, long and unrefreshing.2 Patients may also report prolonged difficulty waking with automatic behavior, confusion, and repeated returns to sleep, a symptom named “sleep drunkenness.” Several clinical forms have been described,3