Circadian Rhythm Sleep Disorders, also known as CRSDs, are disorders related to the timing of a person’s sleep within the 24-hour day. Some of these disorders are influenced by the timing of the sleep period that is under the person’s control (e.g., shift work or time zone change). Others in this group are disorders of neurological mechanisms (e.g., irregular sleep-wake pattern and advanced sleep phase syndrome). There are numerous sleep disorders. Some common ones are listed here.

Time-Zone Change (Jet Lag) Syndrome

Jet lag is a condition which is a consequence of alterations in the circadian rhythm. This can result from daylight savings time, shift work, altered day length, or as the name implies, transmeridian travel as on a jet. The condition is generally regarded as being the result of disruption of the “light/dark” cycle that governs the body’s circadian rhythm. When traveling across a number of time zones, the body’s internal clock becomes out of sync with the destination time, and so it experiences daylight and darkness contrary to the rhythms to which it has grown accustomed.

Shift Work Sleep Disorder

Shift work is an employment practice designed to make use of the 24 hours of the clock, rather than a standard working day. The day is commonly divided into three eight-hour shifts (first shift, second or “swing” shift, and third, or “graveyard” shift). Shift work sleep disorder is a disorder that affects people who change their work or sleep schedules frequently. Such recurrent interruption of sleep patterns may result in insomnia and/or excessive sleepiness.

Irregular Sleep-Wake Pattern

People with irregular sleep-wake syndrome may complain of either insomnia or excessive sleepiness. These individuals usually report an irregular pattern of at least three sleep episodes during a 24-hour period. Total sleep time is normal for age. No underlying medical or mental disorder accounts for these symptoms, and no other sleep disorder is generally present. Most people experience occasional disturbances in their sleep habits. However, this type of irregular sleep-wake pattern occurs regularly and spontaneously, and people with this occurrence may consider consulting a physician. These individuals may often find themselves tired during the day because they nap so much. During the night, they may seem to have insomnia because they are awake for long periods of time at night.

Delayed Sleep-Phase Syndrome

Delayed sleep-phase syndrome, or DSPS, is a chronic disorder of sleep timing. People with DSPS tend to fall asleep at very late hours, and also have difficulty waking up in time for work or school. Often, these individuals report that they cannot sleep until early morning. Unlike people with insomnia, however, they fall asleep around the same time every night, no matter what time they go to bed. Unless they have another sleep disorder, such as sleep apnea, in addition to DSPS, they can sleep well and have a normal need for sleep. The disorder usually develops in adolescence or early childhood, and often disappears in adolescence or early adulthood. It is normally treatable, but not curable.

Advanced Sleep-Phase Syndrome

Advanced sleep-phase syndrome (ASPS) is a disorder in which people feel very sleep early in the evening (e.g. 6 or 7pm) and wake up very early in the night (perhaps midnight or 1am). It is effectively the opposite of DSPS. ASPS is frequently encountered in older adults and post-menopausal women. It can be treated pharmacologically, with evening bright lights, or behaviorally with chronotherapy or free-running sleep.

Non-24-hour Sleep-Wake Syndrome

Non-24-hour sleep-wake syndrome is a disorder in which a person’s internal clock runs longer than 24 hours. The person’s body essentially insists that the day is longer than 24 hours, which may not allow socially accepted sleeping patterns and make it hard to sleep at “normal times.” Untreated, the syndrome causes a person’s sleep-wake cycle to change daily. The cycle may go around the clock, eventually returning to “normal” for a day or two before going “off” again. This is known as “free-running” sleep. Common treatments are similar to those for DSPS, including light therapy, vitamin B12 supplements, and melatonin supplements. The treatment, however, is not a cure, and the disorder can only be managed.

Normal Circadian Rhythms

Among individuals with healthy circadian clocks, there are “morning people” and “night owls.” Whether “larks” or “owls,” people with normal circadian rhythms are able to wake in time for what they need to do in the morning, and fall asleep at night in time to get enough sleep before getting up. These people can sleep and wake at the same time every day if they want to, and if they start a new routine that requires them to wake up earlier, they will start to fall asleep earlier at night within a few days. To maintain a 24-hour day/night cycle, the body’s biological clock needs regular environmental time cues, such as sunrise, sunset, and daily routines. These cues keep the normal human circadian clock aligned with the rest of the world.

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