Sleepiness can be due to the body’s natural daily sleep-wake cycles, inadequate sleep, sleep disorders, or certain drugs.
Each day there are two periods when the body experiences a natural tendency toward sleepiness: during the late night hours (generally between midnight and 7 a.m.) and again during the midafternoon (generally between 1 p.m. and 4 p.m.). If people are awake during these times, they have a higher risk of falling asleep unintentionally, especially if they haven’t been getting enough sleep.
The amount of sleep needed each night varies among people. Each person needs a particular amount of sleep in order to be fully alert throughout the day. Research has shown that when healthy adults are allowed to sleep unrestricted, the average time slept is 8 to 8.5 hours. Some people need more than that to avoid problem sleepiness; others need less.
If a person does not get enough sleep, even on one night, a “sleep debt” begins to build and increases until enough sleep is obtained. Problem sleepiness occurs as the debt accumulates. Many people do not get enough sleep during the work week and then sleep longer on the weekends or days off to reduce their sleep debt. If too much sleep has been lost, sleeping in on the weekend may not completely reverse the effects of not getting enough sleep during the week.
Certain medical conditions and drugs, including prescription medications, can also disrupt sleep and cause problem sleepiness. Examples include:
Read more articles on Sleep Disorders.