Stages of Sleep: What Happens While You Are Sleeping

What is meant by stages of sleep? Isn’t sleep one long continuous state which begins when you fall asleep and lasts till you wake up? If you are under the impression that one can only be ‘productive’ while awake, think again. One-third of our lives that we spend sleeping directly impact on how full, energetic and healthy the balance two-thirds of our lives can be.

Stages of sleep: what they mean and what they are? 

Sleep, is essentially a series of stages of sleep that repeats several times during the night. Each stage is different in terms of the roles they play in preparing the mind and body to function optimally. It goes without saying that each of these stages is as important as the other for keeping a healthy mind and body.

The two main types of sleep are: 

  1. Non-REM or NREM that is made up of four stages, where each stage is deeper than the previous.
  2. REM or Rapid Eye Movement is the stage when most dreams occur. Because eye movement is rapid during this stage, hence the name.

Sleep pattern 

The structure of sleep is such that there is an alternating pattern between NREM and REM in the form of a recurrent cycle that happens every 90 minutes or so. This happens throughout the night (4 to 6 times) following a predictable pattern shifting between deep sleep and more alert and dreaming stages (REM). A complete sleep cycle is made up of both these stages combined.

The amount of time spent in each stage varies as the night progresses. For example, the deepest sleep happens during the first half of the night.

What happens during the different stages of sleep? 

With the onset of sleep, we enter the NREM stage (makes up for 75% of the night) which consists of 4 stages. Here is what happens during these 4 stages:

  1. Stage 1 (Transition of sleep): This is between being awake and falling asleep; light sleep. It lasts for about 5 minutes. Muscular movements slow down and the individual can be woken up easily.
  2. Stage 2(Light sleep): marked by onset of sleep; gradual disengagement from surroundings; heart rate regular; drop in body temperature. It lasts for about 10 to 25 minutes.
  3. Stages 3 and 4: Deepest and most restorative stages when it is difficult to wake up; drop in blood pressure; slower breathing; muscle relaxed; blood supply to muscles increase; time for tissue growth and body repair; time for energy restoration; release of growth hormone and time for muscular development.

The REM stage that covers 25% of the night first occurs close to 70 to 90 minutes after onset of sleep and keeps on repeating every 90 minutes thereon. However its duration gets longer in the night.

Events that happen during such stages of sleep are: 

–          Energy supply to brain and body

–          Dreaming

–          Shallow breathing

–          Building a supportive environment for daytime performance

–          Brain is active; heart rate and blood pressure increase

–          Eyes move back and forth

–          Body is immobile with muscle paralysis of arms and legs.

–          Additionally, cortisol hormone reduces at bed time and increases during the night to improve daytime alertness.

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