What is Idiopathic Hypersomnia/Hypersomnolence

Idiopathic Hypersomnia (IH) is a rare neurological sleep disorder. In 1976 Bedrich Roth coined the term "Idiopathic Hypersomnia" and defined two forms of the disease, Monosymptomatic (previously referred as “without long sleep”) manifested by excessive daytime sleep/sleepiness, and Polysymptomatic (previously referred to as “with long sleep”). This is characterised by exceptionally deep and abnormally long nocturnal and daytime sleep, great difficulty awakening and "sleep drunkenness" (sleep inertia). Recent research supports the findings of previous studies that suggest Polysymptomatic Idiopathic Hypersomnia is distinct and unique and is in fact an independent sleep disorder of Monosymptomatic Idiopathic Hypersomnia. The research showed that the clinical features of Monosymptomatic Idiopathic Hypersomnia were more closely related to those found in Narcolepsy without cataplexy (Type 2 Narcolepsy). Below is a more detailed description of Polysymptomatic Idiopathic Hypersomnia.

Despite sleeping as much or even more than 10 hours a night people with Polysymptomatic Idiopathic Hypersomnia typically also have abnormally long daytime naps. They also experience sleep inertia also known as sleep drunkenness (significant difficulty in coming to complete wakefulness accompanied by confusion, disorientation, poor motor coordination, blurred vision, difficulty expressing & understanding verbal communication, slowness, and repeated returns to sleep) upon awakening. Patients find waking from sleep extremely difficult and can sleep through several alarm clocks, even physical attempts by friends/family to wake them may fail.  

Even though these patients have excessive amounts of good quality sleep patients with Polysymptomatic Idiopathic Hypersomnia wake up unrefreshed and are in an almost constant state of sleepiness. Patients experience these symptoms continually for years. Polysymptomatic Idiopathic Hypersomnia is a lifelong disorder. Symptoms typically begin in adolescence or young adulthood. Polysymptomatic Idiopathic Hypersomnia is debilitating as patients spend the majority of their life either asleep or barely awake. The impaired cognitive ability*, the excessive sleep, and continuous feeling of never being fully awake profoundly affects work, education, and quality of life and leaves sufferers at risk of potentially life-threatening accidents. In addition, some patients exhibit hypersensitivity to sedating medications such as anaesthetics, sleeping pills, or alcohol. The cause of Polysymptomatic Idiopathic Hypersomnia is unknown however it is thought to be caused by a dysfunction of part of the brain that regulates sleep and wake. Some researchers also believe there is a genetic link. Further research is required. For more information and a description of Monosymptomatic Idiopathic Hypersomnia

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*cognition is a group of mental processes that include attention, memory, producing and understanding language, learning, reasoning, problem solving and decision making. 


▪Šonka K, Susta M, Billiard M Sleep Medicine Dec 2014 Narcolepsy with and without cataplexy, idiopathic hypersomnia with and without long sleep time: a cluster analysis.

. Bassetti, CL & Dauvilliers, Y, ‘Idiopathic Hypersomnia; Principles and Practice of Sleep Medicine (Sixth Edition) 2017’, c 91, pp 883–891.e4  

. Vernet, C & Arnulf, I 2009, ‘Idiopathic Hypersomnia with and without Long Sleep Time: A Controlled Series of 75 Patients’ Sleep Jun 1 2009 

▪Billiard M, Merle C, Carlander B, Ondze B, Alvarez D, Besset A Psychiatry and Clinical Neurosciences 1998 Idiopathic Hypersomnia

▪Roth B, Nevsimalová S, Rechtschaffen A. Hypersomnia with "sleep drunkenness". Arch Gen Psychiatry. May 1972;26(5):456-62.

▪Roth T. Introduction: narcolepsy and excessive daytime sleepiness: from the bench to the bedside. J Clin Psychiatry. 2007;68 Suppl13:4.

▪Roth B. Narcolepsy and hypersomnia: review and classification of 642 personally observed cases. Schweiz Arch Neurol NeurochirPsychiatr. 1976;119(1):31-4

▪Rechtschaffen A, Roth B. Nocturnal sleep of hypersomniacs. Act Nerv Super (Praha). 1969;11(3):229-33.






Dr Anu Bhatia describes the 3 main symptoms of Polysymptomatic Idiopathic Hypersomnia

In this video UK Dr Anu Bhatia describes the three main symptoms of one form of Idiopathic Hypersomnia (Polysymptomatic). Prolonged night time sleep (typically 10-14hrs), great difficultly waking up and feeling unrefreshed and disorientated (sleep drunkenness) and excessive daytime *sleeping* - actually sleeping during the day not just feeling tired.

Not everyone diagnosed with Idiopathic Hypersomnia experiences these extreme symtpoms however Anne, the young women in the video says something most people with Idiopathic Hypersomnia can relate to:
"It's the everyday reality that I just feel I'm not getting as much out of life as I could be, because I'm tired or because I'm sleeping for half the day where I would rather be doing something else."

Is Idiopathic Hypersomnia/Hypersomnolence a Rare Disease?

We are often asked is Hypersomnia/Hypersomnolence a Rare Disease? and the answer is YES IT IS! Check out the Idiopathic Hypersomnolence page on Genetic and Rare Diseases Information Center (GARD).