Understanding How Sleep Works: Non-REM Sleep and REM Sleep

Joseph R. Anticaglia MD
Medical Advisory Board

Healthy sleep is as essential to our wellbeing as is a healthy diet. A massive one third of American adults get inadequate sleep described as less than seven hours of sleep per night In the mid-20th century, many scientists thought the brain to be fundamentally dormant during sleep. Recent studies paint a picture. of the brain’s vibrant activity.

The brain moves through four or five sleep cycles per night. Each cycle lasts approximately 1.5 to 2 hours/. Trained personnel use EEG, (electroencephalography) a non-invasive test, to register recordings of the electrical activity of the brain In addition, the EEG records a person’s eye movements, breathing, heartbeat and muscle activity. The test can be divided into two phases, REM and non- REM sleep with four stages.

A) Non-REM Sleep

Non-rapid eye movement sleep involves the first three stages of sleep. In NREM sleep, the person is going from light to deep sleep. The first two stages are associated with light sleep and the third with deep sleep. In stage three, deep sleep, the vital signs are at their lowest.

Stage 1

This stage refers to a person entering the “twilight zone or drowsy state” of sleep. In this state you’re nodding off to sleep. You’re not completely awake or asleep. During this stage, people may experience “hypnic jerks” or sudden muscle contractions induced by sleep which is nothing to worry about. Muscle movement and eye movement slow down. Stage one lasts five to ten minutes.

Stage 2

A person feels more rested in this light sleep stage which helps renew your energy and prepares you to enter stage 3. The muscles and body relax, the heart rate slows, the body temperature drops and eye movements stop. Stage 2 sleep stage initially lasts about 25 minutes, but its time lengthens with each successive sleep cycle.

Stage 3 (Deep Sleep)

Deep sleep is needed for our physical health. During deep sleep, as the name suggests, it is difficult for someone to awaken you. Loud sounds of a one hundred decibels, for example, made from a lawn mower or jack hammer will not wake some people in this stage

Muscles are completely relaxed and there’s no eye movement. If you awaken a person from deep sleep, the person might need a few minutes to clear the “cobwebs” from his head. This stage commonly lasts 20 to 40 minutes. We get most of our deep sleep in the first four hours of sleep. Sleep walking can happen during deep sleep.

B) REM Sleep (Dream Sleep)

Rapid Eye Movement sleep is needed for our mental and emotional health. REM sleep, stage 4, usually starts about sixty to ninety minutes after falling asleep. The voluntary muscles are immobilized, but the diaphragm (breathing muscle) is functioning and the eyes are moving rapidly.

It’s during this stage the body most closely resembles an awaken state. The brain processes and adds information into memory. The initial REM stage lasts about ten minutes. Each subsequent REM stage gets longer. Most of our REM sleep happens in the second four hours of sleep.

EEG is a tool doctors use to understand the relationship between inadequate sleep and sleep disorders. It helps them manage conditions such as insomnia (trouble falling asleep), narcolepsy (trouble staying awake- sudden onset of sleep), sleep apnea (trouble breathing during sleep), restless leg syndrome, sleepwalking and periodic limb movement.

A good night’s sleep repairs, restores and rejuvenates our body. If you suspect you have a sleep problem, contact a sleep specialist. Many treatments have been successfully used to care for patients with sleep disorders.


  1. National Institutes of Health. Brain Basics Understanding Sleep
  2. National Sleep Foundation; Stages of Sleep
  3. Patel AK et al; Physiology, Sleep Stages; StatPearls Publishing, April 22,2021


REM (rapid eye movement) sleep also called dream sleep, D state sleep, paradox sleep

NREM (non-rapid eye movement) sleep also called S stage sleep

EEG — electroencephalography — measures brain wave activity

Polysomnography — sleep study

Circadian rhythm is your biological internal clock that regulates the sleep-wake cycle and repeats every 24 hours.

Sleep drive is your likelihood of falling asleep at a given time. The more we are awake, the more we experience the gradual increase in the neurotransmitter called adenosine, which drives us towards sleep.

Glymphatic system is the brain’s waste management system. In place of lymphatic vessels, the brain utilizes the glial cells of the central nervous system and perivascular channels to drain away waste proteins and harmful metabolic product, s while simultaneously carrying in nutrients. This activity takes place during Non-REM stage 3 sleep.

This article is intended solely as a learning experience. Please consult your physician for diagnostic and treatment options.