Circadian rhythm sleep disorders

[Tracie Lynn]

Circadian rhythm sleep disorders occur when people’s internal sleep-wake schedule (clock) does not align with the earth’s cycle of darkness (night) and light (day).

Jet lag and shift work commonly disturb the usual rhythms of sleep and waking.
People who have a circadian rhythm sleep disorder cannot awaken or go to sleep at normal hours.
Doctors base the diagnosis on symptoms, sometimes using information from a sleep log and sleep laboratory testing.
Good sleep habits and exposure to bright light initially after waking can help people readjust their sleep-wake cycle.

(See also Overview of Sleep.)
Circadian means around (circa) the day (dies). Circadian rhythms are the regular changes in mental and physical states that occur in about a 24-hour period—a person’s internal clock. These rhythms are controlled by an area of the brain that is influenced by light (called the circadian pacemaker). After entering the eye, light stimulates cells in the back of the eye (retina) to send nerve impulses to this area. These impulses signal the brain to stop producing melatonin, a hormone that promotes sleep.
Normally, people vary in their sleep and wake times. Some people (morning people or larks) prefer to go to sleep and wake early. Others (night people or owls) prefer to go to sleep and wake late. Such variations are not considered a disorder as long as people can do the following:

Wake up when they need to do something in the morning and fall asleep the night before in time to get enough sleep before having to get up
Sleep and wake up at the same time every day, if they want to
Adjust to new sleep and wake times within a few days after they start a new routine

People with a circadian rhythm sleep disorder fall asleep at inappropriate times and then cannot go to sleep or wake up when they need or want to. Their sleep-wake cycle is disrupted.