填空题 Why is it so difficult to fall asleep when you are overtired? There is no one answer that 21 to every individual. But many people fail to note the 22 between fatigue—physical tiredness—and sleepiness, the inability to stay awake. It"s possible to feel "tired" physically and still be unable to fall asleep, because while your body may be exhausted, you don"t feel sleepy. To fall asleep, you need adequate time to unwind, even if you feel fatigued. It"s not so easy to 23 "turn off."
According to Carl E. Hunt, director of the National Centre on Sleep Disorders Research in Bethesda, Maryland, most people do not allow themselves 24 deceleration.
Lack of sleep 25 matters even more. Experts say adults need at least 7 to 8 hours of sleep a night to 26 properly. When you get less sleep than that on 27 nights, you begin to accrue "sleep debt." As sleep debt increases (and functionality decreases), your body experiences a stress response and begins to release adrenaline. Now a vicious cycle has been created: You experience the feeling of being more and more tired, but your body is increasingly stimulated. "Power sleeping" for more hours on weekends is only a 28 solution. "There is no 29 for getting a good night"s sleep on a regular basis," says Hunt.
Most of us, however, don"t get the sleep we need. According to the 2002 National Sleep Foundation, Americans sleep an average of 6.9 hours per night during the week, and 58 percent of adults experience 30 of insomnia a few nights a week or more.
A. adapts B. rarely C. symptoms D. sufficient
E. function F. contemporary G. temporary H. replacement
I. consecutive J. distinctions K. similarities L. substitute
M. complicates N. simply O. applies