About 30 % of adults say they don’t feel rested when they wake up in the morning. They could besuffering from any one of 17 different sleep disorders. In our lecture today, we’re going to examine threeof them: sleep apnea, narcolepsy and insomnia.
    Let’s start with sleep apnea. People who have sleep apnea stop breathing several times a night,sometimes for 10 seconds or longer. And not just once; sometimes from 30 to several hundred times anight. And each time this happens, they wake up and go right back to sleep. So their sleep is constantlyinterrupted. The sleeper is not aware of these interruptions, only of being tired and sleepy the next day. Inaddition, one sign is heavy or loud snoring combined with constant fatigue during the day.
    The cause of this problem is not enough oxygen going through the airway usually because thethroat is too relaxed and blocked. Consequently the treatment is very simple: The person wears a maskattached to a special machine. This ensures continuous, regular breathing throughout the night.
     The second sleep disorder is narcolepsy. Narcoleptic persons get sudden attacks of sleep, in the  middle of the day, any time, any place. They can’t control the attack, so they suddenly fall asleep for briefperiods of time. It comes without warning, due primarily to high levels of certain chemicals in the part ofthe brain that regulates sleep. Once narcolepsy is diagnosed, it’s usually successfully treated withmedication.
    Let’s go on now to the most common sleep disorder, insomnia. Insomnia means difficulty infalling asleep or staying asleep. I am not talking about just occasional difficulties. Insomnia is considereda serious problem when it becomes chronic; that is, when sleeping becomes difficult for several weeks oreven months at a time. The reason could be either physical or psychological. Most often, it ispsychological; that is, it’s caused by stress. Or the cause could be physical, such as too much caffeine ornicotine in your body. Both of these chemicals are stimulants and will keep you from sleeping.
    There are many effective ways to deal with insomnia, some good and some bad. Obviously avoidstimulants like coffee, tea and cigarettes in the evening is a good idea. Some other methods that doctorsrecommend are, first, listening to relaxation CDs or soft music, and second, doing self-hypnosis, whichyou can learn easily with the help of a trained specialist. Then there is always TV—some people findwatching TV helpful. And reading a boring book can be very effective.
51. How many sleep disorders are discussed in the above lecture?
(A) one
(B) two
(C) three
(D) seventeen
(E) eight