Idiopathic hypersomnia (IH) is a chronic neurological disorder marked by an insatiable need to sleep that is not eased by a full night’s slumber. People with idiopathic hypersomnia sleep normal or long amounts of time each night but still feel excessively sleepy during the day. They may take long naps, but wake up feeling no better or worse than when they fell asleep.
The main symptom of IH is excessive daytime sleepiness despite adequate, or more typically, long sleep amounts (e.g., more than 10-11 hours per night). Additional symptoms and complaints commonly include unrefreshing or non-restorative sleep, and sleep inertia and sleep drunkenness. Sleep inertia/drunkenness is the difficulty awakening from sleep, accompanied by feelings of grogginess and disorientation upon awakening.