Everyone needs to sleep, but not everyone needs exactly the same amount to feel rested and refreshed. According to the Centers for Disease Control and Prevention, adults need around seven to eight hours of sleep. Sometimes we have to pull an all-nighter for school or work and we promise ourselves we'll make up the hours over the next few nights, but some people chronically oversleep, or get more than nine hours per night.

The percentage of Americans who are oversleeping increased from 27 to 37 percent from 1985 to 2007, according to a 2013 study. If you're a chronic oversleeper, here are some possible reasons that may explain your condition.

Hypersomnia

According to the American Sleep Association, hypersomnia is when someone shows signs of extreme sleepiness and sleep deprivation and can fall asleep at any given time. Affecting 5 percent of the population, hypersomnia can be separated into two types: primary and secondary. Each type of hypersomnia can be a symptom of another condition.

Secondary hypersomnia, the most common type, can be caused by depression, obesity, epilepsy, or multiple sclerosis. Although primary hypersomnia can be associated with genetic disorders such as myotonic dystrophy, Prader-Willi syndrome, and Norrie disease, it should be noted the hypersomnia could be considered a secondary symptom in several of these cases.

Obstructive Sleep Apnea

Patients who are diagnosed with obstructive sleep apnea (OSA) do not get enough air when they are sleeping. This can cause them to periodically wake up in the middle of the night and feel sleepy during the day, according to the U.S. National Library of Medicine. Because people with OSA can’t fall asleep within the normal sleep cycle, they feel a greater need to sleep, causing them to oversleep, reported CBS News.

Alcohol

According to the Huffington Post, people who consume several alcoholic drinks before sleeping tend to sleep longer than those who sleep normal hours. This occurs because alcohol affects our sleep cycles, creating a desire for us to sleep for longer periods of time. Research from the National Institute on Alcohol Abuse and Alcoholism has shown drinking only a few hours before sleeping causes our sleep to become fragmented and less effective on refreshing our bodies for the next day.