Sleep cycles and what is going on inside while you’re snoozing

This time of year, when we lose daytime light to the dark of night, many people find challenges with sleep. Sleep plays an important role in good health and well-being throughout your life. The way you feel while you are awake depends in part on what happens while you are sleeping. During sleep, your body is working to support healthy brain function and maintain your physical health.

In children and teens, sleep also helps support growth and development. Getting inadequate sleep over time can raise your risk for chronic (long-term) health problems. It can also affect how well you think, react, work, learn, and even get along with others.

A person goes through four to six sleep cycles on an average night. Many have heard of REM, the rapid eye movement stage of sleep where your eyes move and people can see that through your eyelids. But do you know what that really means and, did you know there are actually four stages of sleep?

There are three stages of non-REM (NREM) sleep:

Stage 1, or N1

This stage is the time when you begin to go to sleep, kind of like the ‘dozing off’ period. It lasts typically less than 10 minutes. Your heartbeat, breathing, and eye movements slow. Your muscles relax.  Body and brain activities slow with periods of brief movements, such as twitching. If not disturbed, you move into stage 2, otherwise if disturbed, you’re likely to wake.

Stage 2, or N2

You are officially asleep. Stage 2 accounts for about half of your sleep throughout the night. It lasts for 10-25 minutes during the first sleep cycle, and each stage during the night can become longer. Your body temperature drops and your muscles relax even more than in N1. Brain waves show a new pattern and eye movement stops. Although your brain activity slows, there are short bursts of activity that help resist being woken up by external stimuli like thunder or a car horn.

Stage 3, or N3

This stage is known as your deep sleep, and it is harder to wake someone up in this phase. The body relaxes even further as muscle tone, pulse, and breathing rate decrease. This stage is also referred to as delta sleep or slow-wave sleep (SWS). This is a critical stage, as it allows for body recovery and growth and bolsters the immune system. Some feel this deep sleep contributes to creativity, memory, and shrewd thinking. In the early sleep cycles, N3 stages average 20 – 40 minutes, but get shorter through the night as more time is spent in REM sleep.

Rapid eye movement (REM) sleep

During REM sleep, brain activity picks up, nearing levels seen when you’re awake. At the same time, the body experiences atonia, which is a temporary paralysis of the muscles, with two exceptions: the eyes and the muscles that control breathing. Even though the eyes are closed, they can be seen moving quickly, which is how this stage gets its name. This stage is important to memory, learning, and creativity, and is known for the most vivid dreams (dreams can occur in all stages) due to the increase in brain activity. The REM stage usually begins after you have been sleeping for about an hour and a half and becomes a longer part of each cycle, especially in the second half of the night, becoming about 25% of your total sleep.

In our healthcare environment, non-traditional work hours are necessary for some employees, outside the typical 9 am to 5 pm workday. About 20% of the full-time workforce in the US is involved in some form of shift work, and most average fewer hours of sleep. Shift workers must be willing to make sleep a priority to avoid shift work sleep disorder (SWSD).

The Minnesota Regional Sleep Disorders Center can help with sleep problems by offering sleep studies and testing. They also offer cognitive behavioral therapy for insomnia (CBT-I).