Sleep Disorders: Circadian Rhythm Disorders

Circadian rhythm disorders are disruptions in a person's circadian rhythm -- a name given to the "internal body clock" that regulates the (approximately) 24-hour cycle of biological processes in animals and plants. The term circadian comes from Latin words that literally mean around the day.

Circadian rhythms are important in determining human sleeping patterns. When your body clock gets off schedule, certain problems may develop that affect sleep.

What Causes Circadian Rhythm Disorders?

Circadian rhythm disorders can be caused by many factors, including:

• Shift work
• Pregnancy
• Time zone changes
• Medications
• Changes in routine

Common Circadian Rhythm Disorders

Jet Lag or Rapid Time Zone Change Syndrome: Seen in people who travel across time zones, symptoms include excessive sleepiness and a lack of daytime alertness.

• Shift Work Sleep Disorder: This sleep disorder affects people who frequently rotate shifts or work at night
• Delayed Sleep Phase Syndrome (DSPS): People with DSPS tend to fall asleep late and, as a result, have difficulty waking up in time for work, school, or social engagements.
• Advanced Sleep Phase Syndrome: People with this condition tend to fall asleep early in the evening and wake up earlier than desired in the morning.
• Non 24-Hour Sleep Wake Disorder: Non 24-hour sleep wake disorder is a condition in which an individual has a normal sleep pattern but lives in a 25-hour day. Throughout time the person's sleep cycle will be affected by inconsistent insomnia that occurs at different times each night. People will sometimes fall asleep at a later time and wake up later, and sometimes fall asleep at an earlier time and wake up earlier.

Reviewed by The Sleep Medicine Center at The Cleveland Clinic.