The most common cause of excessive daytime sleepiness is not sleeping long enough. If you are still excessively sleepy during the day after getting 7.5 to 8 hours of sleep each night for 7 to 10 days, other things may be causing your sleep problem.

Excessive sleepiness can be caused by a number of medications. If you take any medications, it would be wise to discuss your sleepiness with the prescribing physician to see if a change in medication would help. If a change in medication doesn't help, or if your medications do not usually cause sleepiness, you may have a sleep disorder.

Excessive sleepiness is dangerous. It makes a person as unsafe behind the wheel as one who is drunk. Because sleepiness decreases our attention to details, it can result in accidents while operating equipment. Some medical causes of daytime sleepiness may also lead to high blood pressure, congestive heart failure, memory problems, emotional or personality changes, and even strokes.

Obstructive Sleep Apnea, Narcolepsy and Restless Leg Syndrome.

Common medical conditions that cause excessive sleepiness include obstructive sleep apnea, narcolepsy and restless leg syndrome.