Definition - What does Sleep Cycle mean?

Sleep cycle refers to the pattern of sleep stages that a person progresses through when sleeping. A full sleep cycle includes several different stages, each characterized by a different brain wave pattern. While sleep cycles for adults may last between 70 and 120 minutes, the initial sleep cycle of a sleep period is usually shorter than later cycles.

The sleep cycle may also be called the NREM-REM cycle.

SureHire explains Sleep Cycle

A single sleep cycle will include a set of sleep stages. The cycle begins as a sleeper transitions from wakefulness to sleep. This stage is a non-rapid eye movement stage and is called N1 or NREM1. Following this transitional phase, the sleeper's heart rate slows and body temperature will drop and he or she enters NREM2, also known as N2 or Stage 2. Stage 3 sleep is a deep sleep from which it is difficult to rouse the sleeper. This stage is characterized by delta brain waves. Each period of delta stage sleep in the cycle becomes progressively shorter throughout the night.

Rapid eye movement or REM sleep is the fourth stage in the sleep cycle. During the first sleep cycle, REM sleep may last for only 10 minutes but can last for as long as one hour during later sleep cycles occurring during the same sleep period. During REM sleep, the sleeper is fully asleep but their brain waves indicate high levels of activity and their heart rate and breathing are quickened.

An individual who experiences disrupted sleep cycles may suffer from daytime sleepiness or other signs of sleep deprivation. Disorders related to the sleep cycle are often called circadian rhythm sleep disorders or sleep/wake cycle disorders.

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