Insomnia and excessive daytime sleepiness (eds)

[Rihanna]

The most commonly reported sleep-related problems are insomnia and excessive daytime sleepiness.

Insomnia is difficulty falling asleep or staying asleep, waking up early, or a disturbance in sleep quality that makes sleep seem inadequate or unrefreshing.
Excessive daytime sleepiness refers to being unusually sleepy or falling asleep during the day.

(See also Overview of Sleep.)
Difficulty falling and staying asleep and waking up earlier than desired are common among young and old. About 10% of adults have long-standing (chronic) insomnia, and about 30 to 50% sometimes have insomnia.
When sleep is disturbed, people sometimes cannot function normally during the day. People with insomnia or excessive daytime sleepiness are sleepy, tired, and irritable during the day and have trouble concentrating and functioning. People with excessive daytime sleepiness may fall asleep when working or driving.
There are different types of insomnia:

Difficulty falling asleep (sleep-onset insomnia): Commonly, people have difficulty falling asleep when they cannot let their mind relax and they continue to think and worry. Sometimes the body is not ready for sleep at what is considered a usual time for sleep. That is, the body’s internal clock is out of sync with the earth’s cycle of light and dark—as can occur with many types of circadian rhythm sleep disorders, such as delayed sleep phase disorder, shift work disorder, and jet lag.
Difficulty staying asleep and waking up earlier than desired (sleep maintenance insomnia): People with this type of insomnia fall asleep normally but wake up several hours later and cannot fall asleep again easily. Sometimes they drift in and out of a restless, unsatisfactory sleep. Sleep maintenance insomnia is more common among older people, who are more likely to have difficulty staying asleep than are younger people. It may occur in people who use certain substances (such as caffeine, alcohol, or tobacco) or who take certain drugs and in people who have certain sleep disorders (such as sleep apnea or periodic limb movement disorder). This type of insomnia may be a sign of depression in people of any age.