Idiopathic Hypersomnia by Dr. Zorn.
Idiopathic Hypersomnia is a rare condition of unknown etiology. It is thus like what Narcolepsy was over 20 years ago until researchers discovered that Narcolepsy was due to a deficiency of an excitatory neurotransmitter called orexin.
Like Narcolepsy, Idiopathic Hypersomnia tends to have its onset in the teen's or twenties and has an association with excessive sleepiness.
Because the cause is (at yet) unknown, Idiopathic Hypersomnia is a diagnosis of exclusion. This means that other causes of excessive sleepiness much be ruled out first.
It is characterized clinically by excessive daytime sleepiness with long and un-refreshing naps, prolonged and undisturbed nocturnal sleep, and often great difficulty waking up and "getting going" (sleep drunkenness) after sleep.
It differs from Narcolepsy in that there is an absence of cataplexy and less than 2 sleep onset REM naps on MSLT studies. Cataplexy is a condition of sudden loss of muscle tone during periods of emotion (such as during laughter.) It also differs in that 25% of Idiopathic Hypersomnia patients have a resolution of their sleepiness with time.
The treatment of Idiopathic Hypersomnia is with stimulants.