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The Sleep Cycle


Written by Lanna Wei


Sleep Cycles

Sleep is the most rewarding way to wind down, relaxing your body and mind after a long day at school or work. But have you ever wondered what exactly happens during these long hours? Normally, your body will process through 4-6 cycles, each one lasting around 90 minutes, but it could vary depending on factors such as age, alcohol/drug consumption, along with whether the person has a sleeping disorder (ex. insomnia).

For each cycle your body goes through during a night of sleep, you also transition through four different stages. The first three stages are known as non-REM (non-rapid-eye movement) sleep, and the higher the stage of non-REM sleep it is, the harder it is for someone to wake up because they’re in a deeper sleep. The final and last stage is known as REM sleep, named because this is the stage where your eyes rapidly move back and forth (creepy)! You typically transition into this stage after being asleep for at least 1.5 hours.

During the first cycle of the night, you transition slowly through all four of these stages in order, or chronologically. Afterwards, depending on your body, you might skip through certain stages and transition into deeper sleep. Everybody’s body changes through these stages and cycles during the night, and the pace or way it happens fits to adjust each person individually.


The Four Stages

Stage 1 Non-REM Sleep:

  • During the first stage of this sleep, your body and brain begin to slow down (along with twitches of movement) and shift from being awake to light dozing.

  • Usually lasting 5-10 minutes, a person left undisturbed will shift into Stage 2 of Non-REM sleep, however if awoken, it typically will feel like you haven’t slept at all.

Stage 2 Non-REM Sleep:

  • Now, your body and heart rate slow down even further, and you’re beginning to transition into a deeper sleep. It begins to prepare you for REM sleep, and your muscles will relax and body temp will drop.

  • Around 50% of your night’s sleep is spent here in Stage 2, with each cycle lasting from 30 minutes to an hour in length.

Stage 3 Non-REM Sleep:

  • As the beginning of deep sleep, this stage is important because it allows one to feel refreshed instead of groggy when waking up in the morning. However, Stage 3 is also known as delta sleep or slow-wave sleep due to the specific patterns that are emitted in the brain.

  • While in this phase, your breathing and heartbeat slows down the most and your muscles relax even further, making it increasingly difficult to wake up someone that’s sleeping. Around 20-40 minutes is spent in Stage 3 sleep per cycle.

Stage 4 REM sleep:

  • Starting from this stage, your brain activity quickly begins to increase- almost close enough to the levels if you were awake, and this causes vivid dreams. At the same time, your body (except for your eyes, hence the name, and muscles that control breathing) also become “paralyzed”- known as atonia. Heartbeat, breathing, and blood pressure increase during this time also.

  • REM sleep is believed to boost functions such as memory, creativity, etc, and people also spend less and less time in this stage as they become older in age.

Sources

https://www.sleepfoundation.org/stages-of-sleep

https://www.everydayhealth.com/sleep/sleep-cycles-and-the-stages-of-sleep/

https://my.clevelandclinic.org/health/articles/12148-sleep-basics

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