Idiopathic hypersomnia (IH) is a rare disorder (the exact prevalence is not known) characterized by chronic non-imperative sleepiness in association with long unrefreshing daytime naps. Most of cases present diffi culties reaching full alertness after awakening, even after napping with symptoms of sleep drunkenness (sleep inertia).
According to ICSD [ 3 ], four diagnostic criteria must be met:
- The patient has daily periods of irrepressible need to sleep or daytime lapses into sleep occurring for at least 3 months.
- Cataplexy is absent.
- An MSLT performed according to standard techniques shows fewer than two sleep-onset REM periods.
- The presence of at least one of the following:
- The MSLT shows a mean sleep latency of ≤8 min.
- A total 24-h sleep time is ≥660 min (typically 12–14 h) on 24-h polysomnographic
- monitoring (performed after correction of chronic sleep deprivation) or by wrist actigraphy in association with a sleep log (average over at least 7 days with unrestricted sleep).
- Insufficient sleep syndrome is ruled out.
- The hypersomnolence and/or MSLT findings are not better explained by another sleep disorder, other medical or psychiatric disorders, or use of drugs or medications.