When it comes to sleep, we’re so occupied with our dreams and checking out of consciousness for the day that we sometimes forget that our bodies never really power down — they are constantly working, even while we are in our deepest sleep.

When our bodies enter that stage during the night, our blood pressure drops, our breathing slows, our muscles relax and hormones, including those that help us grow and develop, are released, according to the National Sleep Foundation. The rapid eye movement stage is also when our muscles are “turned off,” which makes our bodies immobile.

But lots of other processes are at work too.

1. Hunger Hormones

As we snooze, our digestive systems continue regulating levels of the hormones leptin and ghrelin. Leptin helps “inhibit hunger and regulate energy balance” while ghrelin does almost the opposite, stimulating appetite and controlling the release of insulin, according to the Hormone Health Network.

When we don’t get enough pillow time, it can throw off the balance of these hormones, which could explain why people can get pretty ravenous the day after a sleepless night.

2. In Your Eyes

Sleeping eyes are famous for rapid eye movement, but they are even busier than that. The crusties or mucus that accumulate in their corners overnight come from our eyelids cleaning us out.

The “discarded cells, mucus and debris (including bacteria, bits of oil from the eyelids, and dust) ... are collected as the eyelids sweep across the eye,” opthalmologist Dr. Ivan Schwab told the Huffington Post. “Our eyelids close similarly to a zipper, from the cheek side toward the nose. When they do that, they push the tears across the eye, picking up all these different materials along the way.”

3. Body Repairman

Sleep is about repairing the body, so our body releases human growth hormone when get catch some shuteye to help grow and repair muscles and bones. “Every tissue in the body is renewed faster during sleep than at any time when awake,” according to a report in the Daily Mail. Our bodies also produce testosterone and fertility hormones.

As a bonus, sleep relaxes our muscles to further allow for restoration.

4. Ready For A Fight

Taking a trip to dreamland boosts our immune system because it releases certain proteins that help us fight off infection, including an agent called tumor necrosis factor that might kill some types of tumor cells, the National Cancer Institute says.

“Some studies of healthy young adults have shown that moderate amounts of sleep deprivation reduce the levels of white blood cells which form part of the body's defense system,” according to the Daily Mail. “Research has shown that people who stayed up until 3 a.m. had one-third fewer cells containing [tumor necrosis factor] the next day, and that the effectiveness of those remaining was greatly reduced.”

5. Don’t Stress Out

When we hit the sack, our body lowers its levels of cortisol, a steroid hormone linked to stress, among many other functions, like regulating the cardiovascular system. When its levels are too high, according to the Hormone Health Network, it can “contribute to changes in a woman's libido and menstrual cycle” and might be linked to anxiety and depression.

6. I Feel Pretty

Similar to how our muscles repair themselves as we sleep, our skin works on restoration of its own. More skin cells are produced and the skin slows down its breakdown of proteins, allowing greater growth and repair. “Deep sleep may indeed be beauty sleep,” the Daily Mail says.

But it has to be at night, not a daytime nap: “The energy needed for tissue repair is not available during daylight because it is being used elsewhere.”

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