Judging from recent surveys, most experts in sleep behavior. agree that there is virtually an epidemic of sleepiness in the nation. 'I can't think of a single study that hasn't found Americans getting 【C1】______ sleep than they ought to.' says Dr. David. 【C2】______ people who think they are Sleeping enough would probably be better 【C3】______ with more rest. The beginning of our sleep deficit crisis can be 【C4】______ to the invention of the light bulb a century ago. From diary entries and other personal 【C5】______ from the 18th and 19th centuries, sleep scientists have reached the 【C6】______ that the average person used to sleep about 9.5 hours a night. 'The best sleep habits once were 【C7】______ on us, when we had nothing to do in the evening down on the farm, and it was dark.' By the 1950s and 1960s, that sleep schedule had been reduced 【C8】______ , to between 7.5 and 8 hours, and most people had to wake to an alarm clock. 'People cheat on their sleep, and they don't even 【C9】______ they're doing it,' says Dr. David. 'They think they're okay because they can get 【C10】______ on 6.5 hours, when they really need 7.5, 8 or even more to feel ideally 【C11】______ ' Perhaps the most merciless robber of sleep, researchers say, is the 【C12】______ of the day. Whenever pressures from work, family, friends and community 【C13】______ , many people consider sleep the least 【C14】______ item on the agenda. 'In our soci-ety, you're considered 【C15】______ it' you say you only need 5.5 hours' sleep. If yon say you've got to get 8.5 hours, people think you lack 【C16】______ and ambition.' To assess the 【C17】______ of sleep deficit, researchers have put subjects 【C18】______ a set of psychological and performance tests requiring them, for instance, to add columns of numbers or recall a passage read to them only minutes earlier. 'We've found that if you're sleep-deprived, performance 【C19】______ ,' says Dr. David. 'Short-term memory is impaired, 【C20】______ are abilities to make decisions and to concentrate.' 【C1】