When you fall asleep into sweet slumber, you might not realize it but there is still a lot of activity going on in the brain. There are actually stages through which the sleep cycle progresses over the course of the night. This was first analyzed through the invention of the electroencephalograph.


The study of sleep revealed that there are basically two broad types of sleep. These include:

  • NREM or Non Rapid Eye Movement sleep or Quiet sleep.
  • REM or Rapid Eye Movement sleep, which is also referred to as paradoxical sleep or active sleep.


Stages of sleep

In the initial phase of sleep when one is still alert, the brain produces fast to small beta waves. As the brain slows down, alpha waves are produced. Also, hypnagogic hallucinations and myoclonic jerks are experienced in this phase.


Sleep is categorized into the following 4 stages:

  • NREM Stage 1

This stage is a transition state between being awake and asleep. This period of sleep lasts only about 5 to 10 minutes, and high amplitude theta brain waves are produced in this stage.


  • NREM Stage 2

In this stage, the brain produces rhythmic, rapid “sleep spindles.” Also, there is a drop in body temperature in this stage along with regular breathing and heart rate. People experience less awareness of their surroundings in this phase and spend close to 50% of their sleep in this phase.


  • NREM Stage 3

This is a transition state between light sleep and deep sleep, and in this phase delta waves are produced by the brain. In this stage there is a drop in the breathing rate and blood pressure, the muscles relax, and deep sleep is experienced in this period.


  • REM Stage

This stage is characterized by an increase in brain activity as well as respiration rate along with increased eye movement. The muscles, on the other hand, become more relaxed and immobilized. Dreams occur in this paradoxical phase, and this stage makes up approximately 20% of the entire sleep cycle.


The body enters stage 1 while sleeping, followed by stages 2 and 3. After this, stage 2 is repeated before entering the REM sleep stage. After this, stage 2 is repeated again and this entire cycle repeats about 4 to 5 times during the night.


Best hours of sleep

The body’s circadian rhythms influence the body’s functions, including the sleep and waking cycle, release of hormones, and body temperatures. This circadian rhythm is governed by environmental factors, like the temperature, sunlight, and darkness. Thus in the dark, the body releases melatonin hormones that promote sleep. In the mornings, melatonin levels decrease and cortisol levels rise to provide energy for the day ahead. The level of melatonin decrease is age dependent. Thus, with age people tend to wake up earlier and therefore must accordingly adjust their sleep time in the night to get the required 7 to 9 hours of sleep. After 8:00 p.m. to before midnight is a good time to go to sleep.


Benefits of a nap

A short power nap of 20 to 30 minutes is recommended as it enhances one’s performance throughout the day, makes one alert, lifts one’s mood, and reduces the chances of making mistakes. However, a nap during the day must be short in order to experience the benefits.