When thinking about getting the sleep you need, it’s normal to focus on how many hours of sleep you get. While sleep duration is undoubtedly important, it’s not the only part of the equation.
It’s also critical to think about sleep quality and whether the time spent sleeping is actually restorative. Progressing smoothly multiple times through the sleep cycle, composed of four separate sleep stages, is a vital part of getting truly high-quality rest.
Each sleep stage plays a part in allowing your mind and body to wake up refreshed. Understanding the sleep cycle also helps explain how certain sleep disorders, including insomnia and obstructive sleep apnea can impact a person’s sleep and health.
What Is the Sleep Cycle?
Sleep is not uniform. Instead, over the course of the night, your total sleep is made up of several rounds of the sleep cycle, which is composed of four individual stages. In a typical night, a person goes through four to six sleep cycles1. Not all sleep cycles are the same length, but on average they last about 90 minutes each.
Are All Sleep Cycles the Same?
It is normal for sleep cycles to change2 as you progress through your nightly sleep. The first sleep cycle is often the shortest, ranging from 70-100 minutes, while later cycles tend to fall between 90 and 120 minutes. In addition, the composition of each cycle — how much time is spent in each sleep stage — changes as the night goes along.
Sleep cycles can vary from person to person and from night to night based on a wide range of factors such as age, recent sleep patterns, and alcohol consumption.
What Are the Sleep Stages?
There are four sleep stages3; one for rapid eye movement (REM) sleep and three that form non-REM (NREM) sleep. These stages are determined based on an analysis of brain activity during sleep, which shows distinct patterns that characterize each stage.
|Type of Sleep
|N3, Slow-Wave Sleep (SWS), Delta Sleep, Deep Sleep
The breakdown of a person’s sleep into various cycles and stages is commonly referred to as sleep architecture. If someone has a sleep study, this sleep architecture can be represented visually in a hypnogram.
The classification of sleep stages was updated in 20074 by the American Academy of Sleep Medicine (AASM). Before that, most experts referred to five sleep stages, but today, the AASM definitions of the four stages represent the consensus understanding of the sleep cycle.