Feeling drowsy during the day, sleep deprivation can noticeably affect people’s performance, including their ability to think clearly, react quickly, and form memories.

There are three vital stages of sleep which our body cycles through each night, sometimes several times per night. These stages and cycles support important mental and physical functions which restore and maintain a healthy mind and body, helping us process memory, emotion and information. When we spend the proper amount of time in each stage, we wake feeling refreshed and energized.

Let’s review these stages:

Light Sleep

In this first stage, our bodies relax, our muscles start to loosen up, and our breathing expands.

Deep Sleep

In this second stage, everything slows down so our body (muscles, tissues, organs) and immune system can focus on restoring and recharging.

REM Sleep (Rapid Eye Movement Sleep)

This third stage is where we dream. While we dream, we simultaneously process and store information, making this stage critical for learning and memory. Our brains are active in REM, balancing a dreamy state with absorbing information we’ve been exposed to throughout the day.

This is a powerful stage, hence the expression of wanting to “sleep on it” before making an important decision. It also balances our mood. REM makes up about 25% of our sleep cycle and first occurs 70 to 90 minutes after you fall asleep. Signals are sent to the brain’s cerebral cortex, which is responsible for learning, thinking, and organizing information. Signals are also sent to the spinal cord to shut off movement, creating a temporary inability to move the muscles (“paralysis”) in the arms and legs. Lack of REM sleep has also been linked to certain health conditions, including migraines and irritability.