睡眠与食物和水一样，对我们的精神健康和身体健康至关重要。如果不睡觉，人就会像喝醉酒一样，头重脚轻、反应迟钝、手眼不协调，决策困难、判断失误，甚至连讲话都理不清思路。占据我们生命1/3时间的睡眠对精神、情感、身体健康、免疫力的提高和人体细胞生长、修复起着重要的作用，睡眠时大脑细胞完全休息，大脑功能得到充分保养和恢复。那么，我们到底需要多少睡眠呢？是不是睡得越长越好呢？这篇文章将给您解答这些问题。

The amount of sleep an individual requires varies from person to person, but most adults average eight hours of sleep.

Sleep plays a vital role in our dailyregimen, as during this dormant period, it recharges andrejuvenatesweary body organs and tissues, and restores the body to an alert state. A person's lifestyle is another variable in the amount of time he needs to achieve this healthy balance, and to feel well rested upon awakening.

The quality of a person's sleep also factors into the sleep equation. When we drift off to sleep, we either fall into a deep, restful sleep, or into a shallow, light sleep. One who normally requires eight hours of sleep, but sleeps shallowly, will most likely awaken feeling tired. In contrast, if the same individual sleeps fewer hours, but lapses into a state of deep sleep, he may well awaken refreshed andinvigorated.

A lucky few can bypass shallow sleep altogether, and fall directly into deep sleep on an as needed basis. Alexander the Great's militaryprowessmay have been due, in part, to his ability to take a "cat nap."

Yet one more variable factors into the amount of sleep we require: that of the brain and of the body sleeping simultaneously. Under normal circumstances, the brain's sleep center blocks off the nerves to the brain and to the body to make sleep possible. The brain has no interest in doing anything, and could not even if it did, because the sleep center has shut down the internal organs, the arms, and the legs. Sometimes, however, the sleep center is unsuccessful in shutting down both the brain and the body at the same time. For example, in times of war, it is not unusual for soldiers suffering from sleepdeprivationand from combat fatigue to continue to march, despite the fact that their brains have halted. Thankfully, such a situation is ananomaly, and does not occur with great frequency.

regimen: 生活制度

rejuvenate:使恢复,使年轻

invigorated:精神焕发的

prowess:威力

deprivation:剥夺

anomaly:不正常的