WHY SLEEP?
Yet putting it that way leaves the necessity of the eating, drinking, or sleeping too abstract. If you don't eat or drink for a long time, you don't just feel hungry or thirsty-- long, you start to suffer from malnutrition or dehydration, your body no longer functions normally--too long, and you die. People likewise suffer clear impairment of mental and physical functioning from lack of sleep. Experiments have not been done to demonstrate that enough sleep deprivation can kill people, but have demonstrated that it can kill animals. Failure to "restore homeostatic balance" carries severe penalties!
The harmful effects of depriving a person of sleep are easily demonstrated. As just one illustration, sleep deprived individuals show as much impairment of driving skills as those intoxicated with alcohol; correspondingly, it is estimated that as many auto accidents result from drowsiness as drunkenness. Those who doubt this should consider their comfort with the news from a recent survey (in Accident Analysis & Prevention, 2000;32(4):493-504)of truck drivers finding that nearly half admitted to having fallen asleep behind the wheel!
These effects form part of the basis for claiming a need for, and crucial function of, sleep. Another line of evidence draws on the way the body restores balance after loss of sleep. Just as the starving person, given access to food at last, eats voraciously, or the thirsty person gulps water--often to the point of vomiting it up again--so the sleep-deprived person who finally gets the opportunity to rest sleeps longer, more deeply, and is more difficult to awaken, than would be the case with normal sleep. If awakened before the natural process of sleep restoration has completed its cycle, the sleep-deprived individual will become unusually confused.
You can see this phenomenon emerge in the common practice of "sleeping in late" on weekends and holidays. More dramatically, a person who has gone without sleep entirely for days or weeks will usually sleep for 24 hours at once. In the latter case, most people wouldn't be surprised by this, nor would they consider the severely sleep-deprived person "lazy" or even at liberty to sleep less by an effort of will. In contrast, many people regard the "sleeping in" phenomenon as a habit subject to free will, which they could do without if only they tried hard enough. In other words, there is a widespread refusal to recognize the necessity of making up for lost sleep.
In part this has some
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