Hypersomnia is characterized by episodes of excessive daytime sleepiness or abnormally lengthy nighttime sleep. Regardless of how much sleep they have at night, sufferers feel they simply have to nap during the day, but they never feel refreshed. Hypersomniacs commonly take naps at very inappropriate times.
It is not uncommon for sufferers to sleep for 14 or more hours at a time. Individuals with this disorder may not even begin to enter REM sleep until the normal time to wake up. Hypersomnia most often affects young people and young adults and usually appears before the age of 25.