Sleep phases

The sleep phases there are 4 and when we sleep we can go from one phase to another during the night. Let's start to study the characteristics of each sleep phase and what differentiates them from one another.

Sleep Phase Stage 1

Stage 1 sleep without rapid eye movement (NREM), or sleepless sleep, occurs after you have decided to sleep and your eyes are closed. During this stage, which usually lasts between 1 and 10 minutes, you are lightly asleep and can quickly return to being fully awake.

Definition of characteristics

  • Even if you are asleep, you may wake up feeling like you haven't slept at all.
  • The muscles of your body are not yet inhibited: your eyes roll a little and you can slightly open your eyelids.
  • Your breathing slows down and your heartbeat becomes regular.
  • Blood pressure and brain temperature drop.
  • The hypnotic jerk that we sometimes experience when falling asleep, accompanied or not by the sensation of falling, occurs during this stage. Some say it is a vestigial reflex that humans developed during the evolutionary process to prevent them from falling off the trees in which they slept.

Did you know?

People with irregular sleeping habits tend to have these hypnotic spasms more often.

Sleep Phase Stage 2

When the NREM stage 2 dream kicks in, things get serious!

Definition of characteristics

Stage 2 sleep, which usually lasts about 20 minutes, is characterized by a slow heart rate and a drop in body temperature. Your body slows down to prepare you for deep sleep.

  • It becomes more difficult to wake you up.
  • Your brain begins to emit larger waves.
  • Your blood pressure also decreases and other metabolic functions also decrease.
  • The first two stages of NREM are often called light sleep.

Did you know?

We spend most of our nights in Stage 2 sleep (about 45% of total sleep duration).

Sleep Phase Stage 3

This stage of sleep refers to the combined stages of what was previously separate in stages 3 and 4 of sleep.

Definition of characteristics

  • This stage typically begins 35-45 minutes after falling asleep.
  • As EEGs show, our brain waves slow down and get bigger.
  • At this point, you sleep through most potential sleep disturbances (noises and movements) without showing any reaction.
  • If you actually wake up during NREM Stage sleep, there is a high chance that you will feel disoriented for the first few minutes.

Did you know?

Other names for this stage are "slow wave sleep" and "delta sleep."

Sleep Phase Stage 4

This is the final stage of a standard sleep cycle. The first stage of rapid eye movement (REM) sleep lasts about 10 minutes and usually occurs after you've been asleep for at least 90 minutes.

Definition of characteristics

  • As the name implies, your eyes move rapidly in all directions during Rapid Eye Movement sleep.
  • It is during this stage of sleep (the deepest) that powerful dreams usually occur. The same happens with episodes of sleepwalking and nocturnal enuresis.
  • This stage is also characterized by an increased heart and respiratory rate, and its rhythms can become irregular.
  • The REM stages typically get longer and longer as the night goes on, and the last REM stage can last an hour.

Did you know?

REM sleep is also known as "paradoxical sleep." This is because the brain waves emitted during this stage seem contradictory to sleep: Although you are sleeping, your brain waves are very much like what can be recorded when you are fully awake. Another aspect of this paradox is the fact that even though your brain is more active, most of your muscles are paralyzed.