Every night we close our eyes and go off to another world — the world of sleep. When we awaken, it’s as if we have come back from a journey, except that we don’t know what really happened to us.

We may know we dreamed, or were cold or hot. But what else did we do? What was happening to our body while we slept?

One important thing that happened, of course, was that the muscles of our body relaxed. If someone were to raise our arm gently while we slept, it would be quite limp and we wouldn’t resist. One of the reasons we take a horizontal position when we go to sleep is to allow this muscle relaxation. A set of muscles that doesn’t relax during sleep, however, is around the eyes and the eyelids. These muscles are contracted to keep our eyes closed.

During a night’s sleep, our body does a lot of moving. We may move just one part of the body or another, or turn over completely to change our position. Some people move more, some less, and it also depends on how tired we are, the temperature, what we ate before we went to bed, and so on. The average person moves about 20 to 40 times a night, but we move only about 30 seconds in each hour, or a few minutes in a whole night.

When we are awake, each one of us reacts differently to external events. But when we are asleep, we all react almost in the same way to whatever messages our sense organs pick up. Noise, light, heat, smells produce practically the same reactions in all sleeping persons!

What happens inside our body during sleep? The blood continues to circulate of course, but the heart beat is slower. We breathe more slowly, too, and not as deeply as when awake. Digestion goes on at its usual rate. The liver and kidneys continue working, but at a slightly decreased rate. Our body temperature drops as much as one degree. Perspiring in general may increase, but is less active in the palms of the hands and soles of the feet during sleep than when we are awake.

It is not true, as some people think, that we sleep more deeply at certain times during the night. In any one night, we may go from shallow sleep to deep sleep, over and over again!