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sleep
A periodic state of unconsciousness from which a person or animal can be roused. During an ordinary night's rest there are intervals of deep sleep associated with rapid eye movement (REM). It is during this REM sleep that dreaming occurs. Although its importance remains unclear, regular sleep is essential. Studies have shown that people depreived of sleep become greatly disturbed. Sleep requirement declines in old age. Difficulty in sleeping is called insomnia.
Related entries
• narcolepsy
• sleep apnea
Related category
• ANATOMY AND PHYSIOLOGY
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