The main symptom of Idiopathic Hypersomnia (IH) is excessive deep sleep. Despite adequate and often extraordinary amounts of good quality sleep (eg: 10-11 hours or more per night) people with IH still feel excessively sleepy during the day. Other symptoms typically include:


  • Chronic excessive daytime sleepiness often resulting in long daytime naps.

  • Long and unrefreshing naps. Naps are usually more than one hour long and are typically not refreshing.


  • Extreme and prolonged difficulty awakening from sleep (sleep inertia), accompanied by confusion, disorientation, irritability and poor coordination with an uncontrollable desire to go back to sleep. It can also include automatic behaviour
    ie: performing tasks without consciously knowing it and not remembering you have done them eg: turning off alarm clocks or
    answering your phone. This is known as “sleep drunkenness”.


  • Cognitive dysfunction (commonly referred to as 'brain fog'): problems with memory, automatic behaviour, concentration and attention.

Many people with IH regularly sleep more than 11 hours out of every 24. Despite good quality sleep it is not refreshing. Sleep is deep and waking up can be difficult. Sleep inertia, which is extreme difficulty awakening from sleep can be so severe in people with IH that they sleep through multiple loud alarms and may even fall back to sleep several times. They often require humans to wake them and to make sure they stay awake. Sleep drunkenness is typically experienced with sleep inertia. Sleep drunkenness consists of confusion, disorientation, poor motor coordination, slowness. People with sleep drunkenness may say irrational or unintentional things. Their speech may be slow or slurred. They may be clumsy eg: drop things, walk into doorways or bounce off walls. Some people report sleep drunkenness lasting as much as 4 hours or more and that it can sometimes be more problematic than the chronic daytime sleepiness in IH. Those that experience sleep inertia/sleep drunkenness usually experience it every time they wake up ie: in the morning and when waking up from naps. People with IH commonly say that they never feel awake and that they struggle with a constant mental fogginess that can make carrying out even basic tasks difficult. 

Symptoms frequently appear in the mid-to-late teens or early twenties. IH is a chronic disorder with limited treatment options. Medications do not treat the cause, are often not very effective, and can cause intolerable side effects. Even with medication people with IH may struggle with ordinary day to day activities.

Unlike in other sleep disorders, the sleep in patients with Idiopathic Hypersomnia is normal; there are no disturbances that can account for these symptoms.

Click here to view and download our Idiopathic Hypersomnia Factsheet*. If you are a medical professional and would like free copies of our (trifold) IH information Brochure* for your practice please contact us.

Our Factsheet/Brochure was written by HA's director Michelle Chadwick and has been vetted and is endorsed by Professor Ron Grunstein, MBBS, MD, PhD, FRACP, and international Idiopathic Hypersomnia researcher Professor Karel Šonka MD, DSc.

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