Our bodies operate on a cycle run by an internal body clock, which closely mirrors the length of a full day. This 24-hour cycle is called a circadian rhythm. The term circadian comes from Latin words meaning, “around the day.” Most of us feel alert when it’s light and experience a need to rest when it’s dark. But in circadian rhythm disorders, the body’s internal clock is out of sync with day and night. Thus, normal waking and sleeping times are disrupted.

There are four common circadian rhythm disorders:

• Delayed sleep phase disorder — This is a case in which a person’s normal sleep pattern runs behind, or is delayed from, the socially accepted waking and sleeping times. The desire to go to sleep might not hit until around 2 a.m. or later. When allowed to sleep until fully rested, the waking time would usually be in the afternoon. 
  
  
• Advanced sleep phase disorder — In this disorder, the person’s normal sleep time runs ahead, or is in advance, of what’s considered a normal time to go to sleep. In this case, a person gets very sleepy and goes to bed early, usually between 6 p.m. and 9 p.m. He or she wakes up very early, often 3 – 5 a.m.
  
  
• Jet lag — This is a temporary circadian rhythm disorder in which the body’s wake and sleep signals are in conflict with a new time zone. Alternating sleepiness and insomnia (the inability to sleep) can make it difficult to function for a few days until the body adjusts to the new time. 
  
  
• Shift work sleep disorder — Those who rotate shifts or work nights can experience this disorder. They feel excessively sleepy or experience insomnia because their work schedule conflicts with their body’s internal clock.
  

• Delayed sleep phase disorder — It’s unclear what causes this disorder, but one thought is that the internal clock that regulates body temperature and the output of melatonin (a hormone that influences sleeping and waking patterns) is delayed. The body chemistry that induces sleepiness doesn’t tell you to get sleepy until the early morning hours. Though the disorder tends to run in families, it can occur in those who have experienced head trauma or a serious illness.
  
  
• Advanced sleep phase disorder — This is usually seen among the elderly. One study found several members of an extended family had advanced sleep phase disorder. Such findings could point to a genetic basis for the disorder. Advanced sleep phase disorder also occurs in those who are depressed.
  
  
• Jet lag — This temporary circadian rhythm disruption often results from crossing time zones. It’s most noticeable after crossing three or more time zones.
  
  
• Shift work sleep disorder — The shift worker is forced to work and sleep during times that are not compatible with the circadian rhythm of alertness. leading to fatigue and insomnia.
  

• Delayed sleep phase disorder — Like many bodily systems, circadian rhythm cycles undergo changes during puberty, and delayed sleep phase disorder is most commonly seen among adolescents and college students. It can continue without treatment through adulthood.
  
  
• Advanced sleep phase disorder — This disorder is more likely to appear in the elderly. Researches have yet to pinpoint exactly why this occurs

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There are a number of ways to diagnose and treat circadian rhythm disorders, and treatment varies based on the type of disorder and the degree to which the sleep cycle disruption affects your life. 

• History- A clinical evaluation including a obtaining a thorough history of sleep and wake schedules and symptoms is very helpful in determining whether a circadian disorder may be present. 
• Sleep logs — This is a record of when you go to sleep and when you wake up. Because it’s important to pay attention to the normal wake/sleep cycle, these sleep logs don’t include times of travel or working hours that are not normal for you. 
• Actigraphy — This is a test to measure the wake/sleep cycles over a set amount of time. You wear a small device for about a week on your nondominant wrist (meaning your left wrist if you’re right-handed, and right wrist if you’re left-handed). The device, an actigraph, senses motion and records activity and sleep levels.

• Delayed sleep phase disorder — Work or school may suffer because of excessive sleepiness in the morning. Those with delayed sleep phase disorder find it exceedingly hard to get out of bed. They may be perceived as being lazy, unmotivated and poor performers who are always running late in the morning.
• Advanced sleep phase disorder — Daily life can be greatly impacted by this disorder. Going to bed by 6 p.m. or 7 p.m. cuts into social and family time. People with this disorder who are still working may find their job performance adversely effected if the job requires evening hours.
• Jet lag — For business travelers, jet lag can affect job performance. In today’s world of global business, trips may be scheduled back-to-back to more than one destination and in different time zones. This could result in ongoing sleepiness and insomnia for the duration of the trip.
• Shift work sleep disorder — Data show that shift workers are at increased risk for developing chronic illnesses, including heart disease and troubles related to the gastrointestinal tract. It’s unclear if the higher incidence of chronic illness is because shift workers are awake and active during the night or because they tend to get less sleep than 9-to-5 workers. Fatigue and sleep deprivation can also lead to on-the-job safety hazards.
  

Good sleep hygiene is always important, but it becomes crucial when you’re trying to manage a circadian rhythm disorder.

Good sleep hygiene means that you:

• Get on — and stay on — a regular sleep schedule.
• Avoid alcohol, caffeine and smoking several hours before bed.
• Maintain a comfortable temperature in the room where you sleep.
• Participate in relaxing activities, such as taking a warm bath, before bed.
• Exercise at least 20 minutes per day, four or more hours before going to bed.

Sleep Hygiene Reference Sheet 

More tips:

• Shift work sleep disorder — Other measures to help battle shift work sleep disorder include regulating exposure to dark and light. And, if you’re on a rotating schedule, try to have your new start time follow the direction of the clock (clockwise). If the start time of your new shift is earlier (counterclockwise), there’s a greater chance you’ll feel sleepy, and that could impair job performance.
• Jet lag — To combat jet lag, shift your schedule to the time of your destination a few days before you leave, if possible.
• Advanced and delayed sleep disorder phases — Resetting the body’s clock to alleviate delayed sleep phase disorder or advanced sleep phase disorder usually requires the assistance of a sleep medicine specialist. [link to Circadian Sleep Rhythm Disorder article]