Although sleep can feel like a passive activity, it is actually a very active time for our minds.

Within five different stages, including REM sleep, our bodies heal and process information learned during the day. From memory consolidation, muscle recovery, to hormone regulation, sleep is responsible for many necessary processes that we could not function without. But in order to get the most benefit from your sleep, you need to complete several sleep cycles during the night. Here are the five stages of sleep and how they affect your body and mind:

Sleep Stage 1

The first stage of sleep is known as the transitional stage because it encompasses the time when a person drifts in and out of consciousness. During the first stage muscles tend to jerk and pull you back awake, an experience known as hypnic myoclonia.

This is a non-rapid eye movement (non-REM) stage in which drowsiness gives way to light sleep and is really just a period in which a person winds down and moves into stage two. If you think you may be suffering from disorders like insomnia, establishing good sleep habits like going to bed early and avoiding computer screens at night can help you transition from stage one to stage two more quickly.

Sleep Stage 2

Although this stage is also a time of light sleep, it is also the longest stage of sleep. In fact, 50% of the time spent sleeping is in stage two. During this non-REM stage the heart rate will start slowing down and your core body temperature will decrease. Eye movement also stops and brain waves slow down with occasional waves known as sleep spindles. Muscles will also alternate between tension and relaxation until falling into the deep sleep of stages three and four.

Sleep Stage 3 & 4

The deepest stages of sleep are combined in stages three and four because both stages are characterized by periods of slow wave sleep (SWS). These stages are hardest to wake up from, and if you are woken up during these stages you will often experience feelings of grogginess and disorientation. During these stages, blood flow to the muscles will increase, providing oxygen and nutrients to help muscle recovery.

Stages 3 and 4 are non-REM stages and are mostly responsible for rejuvenating the body. During the slow wave sleep, hormones are released that help replenish muscles that were heavily worked during the day as well as hormones that help regulate appetite. This is why sleep deprivation is related to weight gain and increased appetite.

Sleep Stage 5

We have finally come to the only stage of Rapid Eye Movement. Stage five is different from the other sleep stages because the brain is very active while the body is immobile. In fact, it is called REM sleep because the eyes dart back and forth underneath eyelids while other parts of the body are experiencing temporary paralysis.

Because the brain is active during this stage, this is also the time in which most dreaming occurs. Although stage five REM only accounts for about 20% of total time spent asleep, it is crucial for revitalizing the mind.

A person goes through several rounds of the sleep cycle in one night, and each time the cycle takes a little more time. This allows the brain and body more time to repair and relax, leading to a healthier lifestyle. However, if sleep disorders like insomnia or chronic back pain are causing you to lose precious hours of sleep, your health could be at risk.