Everything to Know About Sleep Cycles

Dr. Colleen Ehrnstrom's profile picture
Dr. Colleen Ehrnstrom, PhD
Dec 27, 20215 min read
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When it comes to getting a good night’s rest, it’s not enough to focus on quantity — it’s also important to consider your sleep quality. The best restorative rest is a complex dance of different sleep stages that shift and expand throughout the night.

What is a Sleep Cycle?

Your body moves through four sleep stages each night. As you leave one stage and enter the next, you experience changes in brain activity as well as body processes like breathing and heart rate.1

One sleep cycle occurs when you progress through all of the sleep stages. This cycle can range from 70 to 90 minutes. Each night, you complete about four to six sleep cycles, which on average takes about 8 hours.1

What are the Sleep Cycle Stages?

The conversation around sleep cycles is complicated by the fact that the numbering of stages has changed in the past few years. Two of the NREM stages (Stages 3 and 4) were combined into one stage and thus, the numbering is different depending on when the information was published. Suffice it to say that there are currently three stages in NREM sleep and one stage in REM sleep. NREM sleep dominates the first half of the night and REM dominates the second half of the night.

The first three sleep stages are non-rapid eye movement (NREM) sleep. Your sleep progresses from light to deep sleep and then back up again. You sleep the most deeply during the last stages of NREM sleep (Stage 3).

Stage 1

When you fall asleep, your brain slips into the first stage of sleep, which lasts just a few minutes. During this stage, your breaths and heartbeat start to slow. Your muscles become more relaxed, but they may wake you if they suddenly jerk or twitch.2

Stage 2

As your body further relaxes and slows, you enter stage 2 of the sleep cycle. Your brain activity diminishes, but occasionally has quick spurts of activity called sleep spindles, which help refresh your brain and process new memories.1,3

Stage 3

Stage 3 sleep is deep sleep that provides quality rest for your mind and body. During this time, your heart rate and breathing become very slow, and your body heals. It becomes more difficult for external disturbances to awaken you when you are in stage 3 sleep.1

These stages are followed by rapid eye movement (REM) sleep, which is the sleep stage during which you have dreams.2 REM sleep stages build on themselves and get longer each cycle.

Stage 4: REM Sleep

The brain becomes very active during the REM sleep stage. Most of your muscles are completely relaxed, but your eye muscles rapidly contract, making your eyes move in multiple directions. Your brain also becomes much more active, leading to vivid dreams.2

Why Are Sleep Cycles Important?

Altogether, the different stages of sleep lead to many important effects within the mind and body, including: 4

  • Resting your heart
  • Healing tissues throughout the body
  • Releasing hormones necessary for growth and fertility
  • Boosting the immune system
  • Supporting learning and remembering
  • Helping you feel well-rested

When you don’t get enough sleep, it can take a big toll. A lack of sleep can affect your mental health, making it harder to think or focus, putting you in a worse mood, and leading to bigger problems like anxiety or depression. People who don’t sleep enough also have a higher risk of developing high blood pressure, heart disease, diabetes, and kidney disease.4

Sleep disorders such as sleep apnea often involve disturbances to the normal sleep cycle. In people with sleep apnea, breathing problems kick in during deep sleep stages, disrupting the stage and making a person fall back into the lighter stages of sleep, where breathing is easier.1 Apnea is a medical condition that is different from insomnia so consult your doctor if you think you have apnea.

Improve Sleep by Focusing on Sleep Cycle Length

Being able to sufficiently move through each of the stages will help you feel better rested. For example, if you are consistently woken during deep stage 3 sleep, you will notice the effects on the way your body feels rested and your mind feels focused.

Practice good sleep hygiene to help reduce unexpected awakenings in the middle of a key sleep stage. Sleep hygiene includes any behaviors and habits that help you promote healthy sleep patterns. Good sleep hygiene can involve:5

  • Ensuring your sleeping area is as comfortable, quiet, and dark as possible
  • Going to bed and waking up at the same time every day
  • Getting in consistent physical activity during the day
  • Eating any large meals earlier in the day, several hours before you go to bed
  • Avoiding alcohol and caffeine, especially in the evenings

Try Cognitive Behavioral Therapy for Insomnia (CBT-I) Today!

When a good night’s sleep is difficult, treatments like cognitive behavioral therapy for insomnia (CBT-I) can help. CBT-I is a form of talking therapy that addresses the root cause of your sleep problems by helping you understand and change your attitude towards sleep. Scientific research has found this treatment to be effective and safe — unlike sleep medications, CBT-I can better address long-term sleep problems and doesn’t lead to addiction or uncomfortable side effects.6

Interested in learning more about CBT-I? Get started with a quick questionnaire to help us better understand where you’re at on your journey to better sleep.


Dr. Colleen Ehrnstrom's profile picture
Dr. Colleen Ehrnstrom, PhD

Dr. Colleen Ehrnstrom is a licensed clinical psychologist with a specialty practice in Acceptance and Commitment Therapy (ACT). Areas of expertise include insomnia and other sleep disorders, anxiety, and depression.

Dr. Ehrnstrom is not a medical provider and is not providing any recommendations regarding medications. Rather, she is sharing and reviewing the research as it relates to education when learning how best to treat insomnia.

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