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Expert Advice, Healthy Living

What Happens to your body while you sleep – or if you don’t?

May 19, 2021

When you drift off to sleep after a long day, your body goes through a series of changes that help your body fully reset and rest. Sleep is essential to allow the brain and body to slow down, recover, and recharge to have a better physical and mental performance the next day. 

So what exactly happens when you sleep? Or worse, what happens to your body when you don’t regularly obtain adequate rest. Let’s take a look: 

There are two basic types of sleep:  

  • Rapid eye movement (REM) sleep and 
  • Non-REM sleep

During a night of sleep, you will go through both non-REM and REM sleep several times, with longer, deeper REM periods happening towards morning. 

Non-REM Sleep Stages

Stage 1 | Stage 1 is a non-REM sleep cycle and is the changeover from wakefulness to sleep.  During this very short period of light sleep, your heartbeat, breathing, and eye movements slow, and your muscles relax with occasional twitches.  Your brain waves also begin to slow from their usual daytime patterns.  

Stage 2 | Stage 2 is a non-REM sleep and is another period of light sleep before you enter deeper sleep.  Your heartbeat and breathing slow, and muscles relax even further.  Your body temperature drops and your eye movements stop.  Brain waves continue to slow down. 

Stage 3 | Stage 3 is a non-REM sleep and is a period of deep sleep that you need to feel refreshed in the morning.  It occurs in longer periods during the first half of the night.  Your heartbeat and breathing slow to their lowest levels during sleep.  Your muscles are relaxed and it may be difficult to awaken you.  Brain waves become even slower. 

When does REM Sleep happen? 

Stage 4 | Stage 4 is REM sleep and first begins about 90 minutes after falling asleep.  As the name sounds, your eyes move rapidly from side to side behind closed eyelids.  Your breathing becomes faster and irregular, and your heart rate and blood pressure increase to near waking levels.  Most of your dreaming occurs during REM sleep, although some can also occur in non-REM sleep.  Your arm and leg muscles become temporarily paralyzed, which prevents you from acting out your dreams.  

It’s important to note that sleep does not actually progress through each of these stages in sequence. Once the body has reached REM sleep, the body cycles through each of these stages about four to five times throughout the night. 

What exactly happens to your body while you sleep through these stages?

One of the most important aspects of sleep is how your hormone levels change. During sleep, several different hormones are released, all with different purposes and functions.

Melatonin is Important 

Melatonin is an important hormone involved with rest and turning off the brain so to speak. It is released by the pineal gland, which helps control your sleep patterns (link my other post of circadian rhythms here). Melatonin is increasing in the body while Cortisol is decreasing. Cortisol peaks during the day as this hormone is important in making the body alert, awake, and ready to take on the day. As we prepare to sleep, cortisol decreases which helps the body get prepared to rest throughout the night. Towards the later hours of sleep, just before you wake up, your cortisol levels will slowly start to increase, getting your body ready to start the cycle all over again. 

During this time, your pituitary gland also releases growth hormones. Growth hormone is important because it helps your body repair itself and grow. 

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