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Amazing Things That Happen When We Sleep

Woman sleeping in a bed in a dark bedroom

Sleep is the ideal way for our bodies to rest. It is a refreshing activity that most of us look forward to in today’s fast-paced environment. But sleep doesn’t just allow bodies to relax. Here are some amazing things that happen to us while we catch some z’s.

Cortisol Levels Drop

Cortisol—the hormone that is released when we are on edge or stressed out—drops during the first few hours of sleep. This is actually a good thing because it would be hard for us to rest properly while our brains—which tell our bodies to stay alert and ready for danger—remain fully active. Cortisol levels increase after we wake up, supplying us with some fresh energy and a healthy appetite soon after leaving our beds.

Other Hormones Are Released

As our cortisol levels drop, other hormones flood our bodies. Melatonin, a hormone that regulates our sleeping-waking cycles, is released into our system as we prepare for sleep. It helps to keep us knocked out until it’s time to rise, and then it begins to leave our systems.

Also, human growth hormone (HGH) is activated throughout our bodies while we sleep, allowing our muscles, bones, and tissue to regenerate. It contributes to cell renewal and physical healing as well.

The antidiuretic hormone (ADH) is released too and controls our need to urinate during the night.

The Brain Processes Information

Sleep is very instrumental in keeping our brains functional. Instead of taking a break during slumber, our brains focus on processing all the information accumulated throughout the day, sorting everything into short-term and long-term memory. The amygdala, a structure in the brain that processes emotion, also becomes very active during Rapid Eye Movement (REM) sleep. While nobody knows the true purpose of dreams, the amygdala’s activity during slumber suggests that dreams are a way our brain works through feelings we have recently experienced.

The Immune System Gets Busy

Sleep is the ultimate recharging method for our immune systems. While we sleep, our immune systems release small proteins called cytokines that fight infection, inflammation, trauma, and stress. Cytokines are both produced and released during sleep, so a lack of rest can put our bodies at a great disadvantage in the war against disease and bacteria. Infection-fighting antibodies are also released when we sleep—although not as many when we don’t get enough of it.

Muscles Are Paralyzed

After we enter REM sleep—the deepest state of sleep that begins about 90 minutes in—the muscles within our limbs are temporarily paralyzed. Some scientists believe that the purpose of this function is to conserve energy, while others think it happens so that we don’t hurt ourselves while dreaming. However, no one knows the exact reason for this type of slumber. The good news is that most people won’t notice this paralysis, because it usually wears off before the brain reawakens. The bad news is that some folks do get the full experience—when their minds are active and awake while their limbs are paralyzed. This can occur immediately after waking up and, although it doesn’t last very long, it can be quite frightening for those who have to deal with it.

Anne Taylor Anne Taylor
Anne Taylor is a writer with a BA in Journalism and a passion for storytelling. Her work has been published on a variety of websites including Listverse and Introvert, Dear, and she is currently working on her first novel. When she's not breaking down complex topics into readable material, she loves to stay on the lighter side and blog about Disney and Universal parks on . Read Full Bio »