The brain has an internal clock that regulates several biorhythms including the timing of an individual’s sleep-wake cycle. In most cases, the environment provides clues in the form of sunlight, activity, and temperature to help align this internal clock with the external environment. In situations when the two clocks are out of sync, individuals have difficulty sleeping during “conventional” sleep hours.
Circadian rhythm disorders can come in a variety of forms based on the pattern of the sleep clock misalignment, including:
- Night owl form (CRD-delayed sleep phase syndrome)
- Morning lark form (CRD-advanced sleep phase syndrome)
- Shift work disorder
- Jet lag
The misalignment between the internal clock and the environment can lead to a number of difficulties including insomnia, daytime sleepiness, and fatigue.