Idiopathic hypersomnia is a chronic condition that results in excessive daytime sleepiness, often combined with long yet non-restorative naps. Despite good-quality – and often prolonged – night-time sleep, the subject has great difficulty waking up in the morning, feels confused and groggy, and can even fall back to sleep. This is called confusional arousal or « sleep drunkenness ». This condition is extremely rare and generally occurs between the ages of 16 and 21. Unlike narcolepsy, IH is characterised by the absence of cataplexy.