Sleep physiology

What happens during sleep?
When we fall asleep our body begins a process of vital cellular repair and regeneration.

Some of these processes are:

  • Repair of cells damaged during the day
  • Stimulation of the immune system
  • Recovery from the day’s activities
  • Recharging the heart and cardiovascular system for the next day

The importance of sleeping well is well known and we all apreciate the feeling of being revitalised after a good night’s sleep and the tiredness after a bad night’s sleep. However, despite knowing this, in the society in which we live we often end up not sleeping the hours that are necessary for our body to carry out all the functions it needs.


An indispensable element for healthy sleep is the correct development of its phases and cycles.

Sleep is made up of four phases, the first three are part of non-REM sleep and can last between 5 and 15 minutes.

NREM sleep is made up of 3 stages:

Stage 1: when your eyes are closed, but it is still easy to wake up
Stage 2: when you are in light sleep. As you prepare for deep sleep, your heart rate decreases and your body temperature drops.
Stage 3: considered the stage of deep sleep. It is more difficult to wake up at this time and if someone wakes you up, you will be more disoriented.

REM sleep is composed of:

Stage 4: REM sleep usually occurs 90 minutes after falling asleep and is the stage of sleep in which we dream. The brain is more active and heart rate and breathing speed up. Adults can spend about 20% of sleep in the REM stage, while babies can spend about 50% of sleep in this stage.

REM stands for Rapid Eye Movement and NREM stands for Non-Removing Eye Movement.

Non REM sleep occurs first, followed by REM sleep and the cycle starts again.

In each cycle the times we stay in the Non REM and REM phases vary, the stay in REM increases in successive cycles.

If during the night the REM and NREM cycles are interrupted several times, either because we snore, have difficulty breathing or wake up frequently during the night, we will impede the vital regeneration processes of our organism, negatively affecting our health in the short and long term.

The differences that exist in each sleep phase are found mainly in the person’s brain activity. For example, the brain waves are slower in deep sleep stages such as 3 and 4. In contrast, in the REM stage, despite being a deep sleep, the brain activity resembles the state of wakefulness, in this stage is when we dream.

Both REM (Rapid Eye Movement) and NREM (Non Rapid Eye Movement) stages are important phases in sleep and serve different functions in your body.
REM sleep, which is when dreaming occurs, helps the mind process emotions, memories and distress and is vital for stimulating the brain.

NREM accounts for 75-80% of total sleep each night. Many of the health benefits of sleep occur during NREM, such as tissue growth and repair. In addition, energy is restored and hormones important for growth and development are released.

Sleep is a vital necessity, but if these hours of sleep are not effective there is no point in being in bed for eight hours.


If we don’t sleep well during the night, going through the REM and non-REM phases, we can present:
• Mood swings, irritability, depression and sleepiness.
• Slowness in the capacity to react, loss of memory, lack of attention.
• Desire to eat foods rich in fats and sugar that can lead to weight gain.