Chronic sleep disorders result from multiple pathophysiological mechanisms and are often associated with severe hypersomnolence, responsible for major disability. Hypersomnolence may be secondary to sleep disturbances at night by sleep fragmentation, both overall in restless leg syndrome (RLS) or specific to slow or paradoxical sleep in parasomnias (sleepwalking, sleep behavior disorder). paradoxical). Attention-Deficit / Hyperactivity Disorder (ADHD) is another cause of secondary hypersomnolence, unsolved pathophysiology, leading to a major disturbance of alertness. More rarely, hypersomnolence may be primary (central hypersomnia), representing then the most severe form existing in humans. The best-known central hypersomnia is narcolepsy type 1 (NT1), affecting 0.02% of the population. It is thanks to the existence of well-characterized clinical, biological and neuropathological patients that its pathophysiology is better understood. It is due to a selective loss of hypothalamic neurons secreting orexin / hypocretin, in connection with a probable autoimmune process, in genetically predisposed subjects. Narcolepsy type 2 (NT2), idiopathic hypersomnia (HI) and Kleine-Levin syndrome (SKL), are rarer forms of central hypersomnia, the pathophysiology of which is still unknown, due to the small number of patients studied.