Idiopathic hypersomnia (IH) is a chronic disabling disorder characterized by excessive daytime sleepiness (EDS), prolonged nighttime sleep and sleep inertia. IH is a rare disorder, estimated around 0.05%, yet its true prevalence remains unknown. Disease onset occurs most often during young adulthood and is accompanied by severe social, professional and economic impairments, resulting in risk of accident and a loss in patient's quality of life. There are no ANSM (or FDA-) approved treatments for IH symptoms.

IH shares common features with delayed sleep-wake phase disorder (DSWPD) which is a chronic circadian rhythm disorder which occurs as in IH during young adulthood. The combination of evening melatonin and morning bright light therapy is the most effective validated chronotherapy in DSWPD.Moreover, bright light therapy has direct effects and is known to increase daytime alertness and to improve mood.

Melatonin is empirically used in routine clinical practice in patients with IH and French and European recommendations mention melatonin as a possible treatment of sleep inertia in IH.

. Our goal is to bring a proof of concept of a safe therapeutic practice for IH combining exogenous melatonin and bright light therapy in