"I want to wake up in a city that never sleeps" is a memorable lyric and great asset for New York. When we think about sleep the consensus would be that nothing goes on in our bodies while doing so other than rest. If you don't marvel at the abilities and complexities of the human body you should take a step back, maybe a couple, and view its capabilities. You'll "find you're King of the hill, top of the heap." You have permission to sing it out!
Fifty years ago sleep was thought to be a relatively dormant time for body & mind. Research now shows that it is anything BUT dormant. About a third of our lives are spent in sleep mode, either REM or non-REM. Want good health? Get a good night's sleep!
The 1st part of the sleep cycle is non-REM which has for phases. The first occurs between being awake and falling asleep. The second is light sleep, when the heart rate and breathing regulate and body temperature drops. The third and fourth stages are deep sleep. REM sleep was previously believed to be the most important sleep phase for learning and memory but now data reveals that non-REM sleep is more important for these tasks, as well as being the more restful and restorative phase of sleep.
REM or Rapid Eye Movement sleep is somewhat like the brain doing a daily backup. It's as active as when we're awake but the body is temporarily paralyzed in a sense. We may cycle though REM and non-REM sleep 4, 5 or 6 times and each session less and less in non-REM.
Two inputs drive our sleep habits. Anything which follows a daily cycle can be said to have a circadian rhythm of light and darkness. Plants, animals, people and even fungus are attuned to it. We also have a sleep drive regulated by melatonin build up as the day progresses. Some may compare the need to sleep to that of hunger the difference being when your mind says sleep you sleep no matter what activity you're in the middle of doing.
Our natural rhythms are constantly being modified through technology in both environmental and nutritional fields. Our biological clocks are changing and adapting. The jury is out whether it's a good or bad thing but know that it's important more than ever to try to get a proper amount of sleep whenever possible.