Idiopathic Hypersomnia (Hypersomnolence Disorder)

Idiopathic Hypersomnia (ICSD-3) or Hypersomnolence Disorder (DSM-5), is a broad diagnosis and includes symptoms of excessive quantity of sleep, deteriorated quality of wakefulness, and sleep inertia. Individuals with this disorder fall asleep quickly and have a high sleep efficiency (>90%). They may have difficulty waking up in the morning, sometimes appearing confused, combative, or ataxic. This prolonged impairment of alertness during the sleep-wake transition is often referred to as sleep inertia (or sleep drunkenness).


Approximately 5%-10% of individuals who consult in sleep disorders clinics with complaints of daytime sleepiness are diagnosed as having hypersomnolence disorder. It is estimated that about 1% of the European and U.S. general population has episodes of sleep inertia. Hypersomnolence occurs with relatively equal frequency in males and females.

Criterion A

Self-reported excessive sleepiness (hypersomnolence) despite a main sleep period lasting at least 7 hours, with at least 1 of the following symptoms:

  1. Recurrent periods of sleep or lapses into sleep within the same day.
  2. A prolonged main sleep episode of more than 9 hours per day that is nonrestorative (i.e., unrefreshing).
  3. Difficulty being fully awake after abrupt awakening
Criterion B

The hypersomnolence occurs at least 3 times per week, for at least 3 months.

Criterion C

The hypersomnolence is accompanied by significant distress or impairment in cognitive, social, occupational, or other important areas of functioning.

Criterion D

The hypersomnolence is not better explained by and does not occur exclusively during the course of another sleep disorder (e.g., narcolepsy, breathing-related sleep disorder, circadian rhythm sleep-wake disorder, or a parasomnia).

Criterion E

The hypersomnolence is not attributable to the physiological effects of a substance (e.g., a drug of abuse, a medication).



Specify if:

  • With mental disorder, including substance use disorders
  • With medical condition
  • With another sleep disorder

Specify if:

  • Acute: Duration of less than 1 month
  • Subacute: Duration of 1-3 months
  • Persistent: Duration of more than 3 months

Severity Specifier

Specify if:

  • Mild: Difficulty maintaining daytime alertness 1-2 days/week
  • Moderate: Difficulty maintaining daytime alertness 3-4 days/week
  • Severe: Difficulty maintaining daytime alertness 5-7 days/week

Specify severity based on degree of difficulty maintaining daytime alertness as manifested by the occurrence of multiple attacks of irresistible sleepiness within any given day occur ring, for example, while sedentary, driving, visiting with friends, or working.

  • Individuals often report constant sleepiness and prolonged naps. The naps are not refreshing. There can often be sleep inertia lasting 2-3 hours in the morning, and individuals may be aggressive in the mornings.
  • Hypersomnolence can be increased temporarily by psychological stress and alcohol use, but they have not been documented as environmental precipitating factors.
  • Viral infections have been reported to have preceded or accompanied hyper somnolence in about 10% of cases. HIV pneumonia, infectious mononucleosis, and Guillain-Barré syndrome, can also evolve into hypersomnolence within months after the infection.
  • Hypersomnolence can also appear within 6-18 months follow ing a head trauma.

Nocturnal polysomnography will show:

  • Normal to prolonged sleep duration, short sleep latency
  • Normal to increased sleep continuity
  • Distribution of rapid eye movement (REM) sleep is also normal
  • Sleep efficiency is mostly greater than 90%. Some individuals with hypersomnolence disorder have increased amounts of slow-wave sleep. The multiple sleep latency test documents sleep tendency, typically indicated by mean sleep latency values of less than 8 minutes.
  • In hypersomnolence disorder, the mean sleep latency is typically less than 10 minutes and frequently 8minutes or less.
  • Sleep-onset REM periods (SOREMPs; i.e., the occurrence of REM sleep within 20 minutes of sleep onset) may be present but occur less than two times in four to five nap opportunities.
  • There are no consistently effective treatments, but modafinil can be used as a wakefulness promoting agent.