This includes treatment for 80% of the 250, 000 to 350, 000 people who suffer from fatigue due to multiple sclerosis, and perhaps 200, 000 of the 12 million patients suffering from obstructive sleep apnea, a sleep disorder that causes a person to stop breathing during the night, but which also causes daytime sleepiness, says Cephalon spokeswoman Sheryl Williams.

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He also says it may be useful for adults with sleep apnea, which causes daytime fatigue and impairs a person's performance.

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Overweight people often have sleep problems -- most notably sleep apnea, a breathing disorder that causes frequent awakenings -- but it's not clear if they're overweight because of their sleep problems, or if their sleep problems result from being overweight.

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Sleep apnea is a disorder that causes people to stop breathing momentarily and wake up as often as hundreds of times every night, leaving a lot of unexplained fatigue, irritability and millions of hours of lost productivity at the workplace.

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According to the American Academy of Sleep Medicine, there are 81 chronic sleeping disorders, from apnea, which causes interrupted breathing, to restless leg syndrome.

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It is the movement of potassium (and also sodium) ions that causes the electrical impulses that nerve cells carry including the impulses found in slow-wave sleep.

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