The introduction about sleep

　　Sleep is a behavioral state that is a natural part of every individual’s life. We spend about one-third of our lives asleep. Nonetheless, people generally know little about the importance of this essential activity. Sleep is not just something to fill time when a person is inactive. Sleep is a required activity, not an option. Even though the precise functions of sleep remain a mystery, sleep is important for normal motor and cognitive function. We all recognize and feel the need to sleep. After sleeping, we recognize changes that have occurred, as we feel rested and more alert. Sleep actually appears to be required for survival. Rats deprived of sleep will die within two to three weeks, a time frame similar to death due to starvation.

It is not normal for a person to be sleepy at times when he or she expects to be awake. Problem sleepiness may be associated with difficulty concentrating, memory lapses, loss of energy, fatigue, lethargy, and emotional instability. The prevalence of problem sleepiness is high and has serious consequences, such as drowsy driving or workplace accidents and errors. Lifestyle factors and undiagnosed or untreated sleep disorders can cause problem sleepiness. Lifestyle factors include not getting enough sleep, having an irregular sleep schedule, and using alcohol or certain medications. Of the more than 70 known sleep disorders, the most common are obstructive sleep apnea, insomnia, narcolepsy, and restless legs syndrome. Large numbers of individuals suffering from these sleep disorders are unaware of—and have not been diagnosed or treated for—their disorder.
Problem sleepiness can be deadly. Approximately 100,000 automobile crashes each year result from drivers who were “asleep at the wheel.” In a survey of drivers in New York State, approximately 25 percent reported they had fallen asleep at the wheel at some time.Crashes in which the driver falls asleep are especially common among young male drivers. One large study found that in over 50 percent of fall-asleep crashes, the driver was 25 years old or younger.In addition to the high risk of automobile crashes, problem sleepiness can cause difficulties with learning, memory, thinking, and feelings, which may lead to poor school and work performance and difficulty with relationships. Furthermore, problem sleepiness leads to errors and accidents in the workplace.
Very few textbooks for high school students provide any scientific information about changes that occur in the body during sleep and how those changes affect our ability to move and think. Of course, we’ve heard that a good night’s sleep will help us perform better on a test the next day, but is this based on scientific fact, or is it just a continuing myth? The lack of information in textbooks may be due to the fact that sleep research is only recently gaining recognition. A great deal remains to be learned through scientific studies, including an answer to the key question, What is the function of sleep? Although its function remains unclear, research is providing a great deal of information about what happens in the brain and body during sleep and how the body regulates sleep.