sleep stages

What are the sleep stages?


There are four sleep stages; One sleep in the rapid eye movement phase (rem) and three non-RAM sleep stages (NREM).

These stages are determined based on an analysis of brain activity during sleep, which shows distinct patterns that characterize each stage.

The analysis of a person's sleep in different cycles and stages is usually called "sleep architecture"; If one is studying sleep, this dream architecture can be shown as a hypnogram.

The classification of sleep stages was updated in 2007 by the American Academy of Sleep Medicine (AASM). Before that, most experts referred to the five stages of sleep, but today the definitions of AASM of the four stages reflect a brief understanding of the sleep cycle.


Sleep Stages

Type of Sleep


Other Names


Normal Length

Stage 1




1_5 miutes

Stage 2




10_60 minutes

Stage 3



N3, Slow-Wave Sleep (SWS), DeltaSleep, Deep Sleep

20_40 minutes

Stage 4



REM Sleep


10_60 minutes





NREM sleep patterns

NREM sleep consists of three different stages. The higher the NREM sleep phase, the easier it is to wake up.


Step 1 / N1

Step 1 is the "snooze" step and usually only takes 1_5 minutes.

During sleep N1, the body is still not completely relaxed, although body and brain activities begin to slow down with short periods of movement (contractions). With sleep, there are light changes in brain activity at this stage.

It is very easy to wake up a person at this stage. But if it does not bother the sleeping person, you can quickly enter stage 2. When night falls; During a period of uninterrupted sleep, a person may not spend as much time in stage 1 as in other stages of the sleep cycle.


Step 2 / N2

In stage 2, the body enters a weaker state, including a decrease in temperature, muscle relaxation, and slowed breathing and heart rate. Meanwhile, the brain waves show a new pattern and the eye stops moving. In general, brain activity slows down, but there is little activity in the brain that helps resist awakening through external stimuli.

Stage 2 in the first sleep cycle can last 10-25 minutes and each N2 stage lasts longer during the night. In total, a person typically spends half of their sleep time in stage N2.


Step 3 / N3

Stage 3 sleep is also known as deep sleep, and it is more difficult to wake up if one is in this stage. With more relaxation of the body, muscle movement, pulse, and respiration rate decrease in stage N3.

Brain activity during this period has a recognizable pattern of delta waves. For this reason, stage 3 can also be called delta sleep or short wave sleep (SWS).

Experts believe that this stage is vital for restorative sleep and improves the body's growth and development. It may also boost the immune system and other important body processes. Even if brain activity decreases, there is evidence that deep sleep contributes to thinking, creativity, and memory.

In the first half of the night, we spend most of our time in deep sleep. In the early stages of sleep, stages N3 usually last 20 to 40 minutes. As you continue to sleep, these steps become shorter, and instead, more time is spent in REM sleep.


REM sleep patterns

During REM sleep, brain activity increases and it is time to wake up. At the same time, the body experiences atony, which is temporary muscle paralysis, except for two: the eyes and the muscles that control breathing. Although the eyes are closed, they can be seen moving fast, which is why this stage is so named.

REM sleep is believed to be essential for cognitive functions such as memory, learning, and creativity. REM sleep is known as true dreams, which is associated with a significant increase in brain activity. Dreams can occur at any stage of sleep, but occur less frequently in NREM periods but are more severe.

Under normal circumstances, you will not enter the REM phase until you have been asleep for about 90 minutes. As the night progresses, the REM stages become longer, especially in the second half of the night. While the first REM step may only take a few minutes, subsequent steps can take about an hour. In total, REM stages make up about 25 percent of adult sleep.