The average amount of daily sleep for young adults is 7.5 hours. However, there is considerable variability in how long people sleep. Sleep needs vary from person to person. Asking how much sleep the average person needs isn't a very useful question, much like asking what shoe size the average person needs. If everyone were given average-size shoes to wear, most people would be very uncomfortable.
Some naps are beneficial and some are not. The effectiveness of napping varies from person to person. Also, the benefits of any specific nap depend on the time of day and the amount ofsleep one has had recently. On the negative side, naps are not very efficient ways to sleep because you're often just getting into the deeper stage of sleep when your nap time is up. Another potential problem is that overly long naps ( more than 2 hours) or naps that occur too close to bedtime can disrupt nighttime sleep. On the positive side, most naps enhance subsequent alertness and reduce sleepiness. Evidence also suggests that naps can help offset the effects of frequent nighttime awakenings in older people. In conclusion, naps can be refreshing for most people, and they can be beneficial in the long run if they don't interfere with nighttime sleep.
Obviously, stimulants such as cocaine and amphetamines make it difficult to sleep. More surprising is the finding that most of the CNS depressants that facilitate sleep (such as alcohol, analgesics, sedatives, and tranquilizers) disrupt the normal sleep cycle. The principal problem is that they reduce the time spent in REM sleep and slow-wave sleep. Unfortunately, these are the sleep stages that appear to be most important to a refreshing night's sleep.
Yawning is a universal human phenomenon seen in all cultural groups. Contrary to popular belief, yawning is not a response to buildup of carbon dioxide or a shortage of oxygen. However, as reputed, yawning is strongly correlated with sleepiness. Whether yawning facilitates or impedes sleep, or has no effect, is not yet known. The most fascinating and perplexing facet of yawning is that it is contagious - seeing others yawn creates a powerful urge to follow suit. Contagious yawning is not well understood, but it is thought to be a neurologically programmed, reflexive response.
|"We all dream; we do not understand our dreams, yet we act as if nothing strange goes on in our sleep minds, strange at least by comparison with the logical, purposeful doings of our minds when we are awake."|