Idiopathic hypersomnia (IH) is a rare sleep disorder that shares many of the symptoms of narcolepsy but is typically characterised by a long sleep duration of 11 hours or more. On awakening, however, people with IH do not feel refreshed and will often experience prolonged periods of confusion, disorientation and irritability known as sleep inertia, a foggy state of mind that can last for several hours. They may also be struck by excessive daytime sleepiness and will need to take naps during the daytime. During periods of sleepiness, it is not uncommon for people with IH to experience automatic behaviour.
Like narcolepsy, symptoms can appear at any age but onset occurs most frequently during the teens and can have a similarly damaging effect on schooling, work and relationships. It is therefore incredibly important to get a diagnosis and treatment as soon after onset of symptoms as possible.
As with narcolepsy, diagnosis will usually require an overnight sleep test and a multiple sleep latency test (MSLT) in a specialist sleep clinic. The treatment of IH involves wake-promoting medications like modafinil and stimulants like methylphenidate. Lifestyle changes can also help, though these can be particularly challenging to implement for people with IH.
The cause of IH is not yet known and there is currently no cure.
Additional information on Idiopathic Hypersomnia can be found from the Hypersomnia Foundation (an American charity but with global outreach)
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