Sodium Oxybate in Idiopathic Hypersomnia

Inclusion Criteria: * Diagnostic of idiopathic hypersomnia (ICSD-3 criteria) * Age between 18 and 60 years-old * BMI between 18 and 35 kg/m2 * MSLT: mean sleep latency (MSL) ≤8 minutes and \< 2 SOREMPs, AND/OR total sleep time \> 11h/24h on 24-hours long-term polysomnography * Polysomnography recording: sleep efficiency \> 85%, total sleep time ≥6 hours, AHI \<10/hour, micro-arousals index \<15/hour, PLM index associated with micro-arousals \<10/hour. * Absence of sleep deprivation, assessed by actigraphy or sleep logs * ESS score ≥14 points * Written informed consent * National health insurance cover Exclusion Criteria: * Current alcohol intake or treatment with modafinil, amphetamine, methylphenidate, mazindol, pitolisant, neuroleptics, sedative hypnotics, barbiturates, general anesthetics, myorelaxants, other CNS depressants, antidepressants\*, anxiolytic drugs, anticonvulsive therapy, topiramate, inhibitors of GHB dehydrogenase (i.e. valproate, ethosuximide, phenytoin), budipine, dopamine antagonist antiemetics (except domperidone), opioids, benzodiazepines, Z-drugs, MAO inhibitors, COMT inhibitors, or sedative antihistamines. If patient has received such therapy, a washout-period of at least 15 days, or equivalent to 5 half-lives of the drug, prior to the inclusion in the study is required before starting treatment in this study. \*30 days for antidepressants * Previous intake of sodium oxybate * Succinic semialdehyde dehydrogenase deficiency, porphyria * Other central nervous system diseases: neurodegenerative diseases, seizure disorders or history of head trauma associated with loss of consciousness * Lifetime history of suicide attempt or suicidal ideation in the past 6 months, prior history of psychotic episodes, current or recent history of a major depressive disorder (DSM-V), Beck depression inventory (BDI) \> 16 and/or item G\> 0 * History of chronic alcohol or drug abuse within the prior 12 months * Malignant neoplastic disease requiring therapy within 12 months prior to Visit 1 or clinically relevant * Heart failure, severe hypertension or other cardiovascular disease compromising the patient's wellbeing or ability to participate in this study * Renal or hepatic impairment Compromised respiratory function * Sleep-related breathing disorders (AHI ≥ 10/h) * No regular sleep at night: shift work or other continuous non-disease-related life conditions * Participation in another study of an investigational drug within the 28 days prior to Visit 1 or currently * Hypersensitivity to any of the components of the study medication * Pregnancy (βHCG positive) and breast-feeding