Hypersomnia (excessive sleepiness) refers to an increased sleep propensity with 
a subjective craving for sleep, involuntary naps and "sleep attacks" during the 
day and/or prolonged nighttime sleep with sleep drunkeness. Excessive sleepiness 
should be separated from fatigue and lack of energy associated with a variety of 
medical and psychiatric diseases. Hypersomnia is reported by 2-5% of the adult 
population and can lead to poor work, accidents and neuropsychiatric 
disturbances. Sleep apnea syndrome (SAS), narcolepsy, chronic sleep deprivation 
(insufficiency), and restless legs/periodic limb movements in sleep syndrome 
(RLS/PLMS) represent the most common causes of hypersomnia. The diagnosis of 
these conditions can often be suspected on clinical grounds. However, an 
overnight polysomnography and a multiple sleep latency test are often 
additionally required for definite diagnosis. Treatment options include nasal 
CPAP for SAS, stimulants for narcolepsy, sleep prolongation for sleep 
insufficiency, and dopaminergic agents for RLS/PLMS.