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        Definition 
        
        | rhythm that completes a full cycle every 24 hours |  
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        Definition 
        
        | deep sleep, occuring during Stage III and especially during Stage IV in NREM sleep |  
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        Definition 
        
        | sleep disorders characterized by insomnia or excessive sleepiness |  
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        Definition 
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        Definition 
        
        | condition characterized by excessive sleeping, especially daytime sleeping |  
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        Definition 
        
        | difficulty in falling asleep |  
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        Term 
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        Definition 
        
        | a natural chemical produced at night that decreases wakefulness and promotes sleep |  
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        Term 
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        Definition 
        
        | condition characterized by an uncontrolled desire to sleep |  
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        Term 
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        Definition 
        
        | condition characterized by marked muscle contaction that results in jerking of one or both legs during sleep |  
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        Definition 
        
        | consists of four stages of sleep where there is very little eye movement |  
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        Term 
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        Definition 
        
        | patterns of waking behavior that appear during sleep (sleep walking, sleep talking) |  
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        Term 
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        Definition 
        
        | stage that constitutes 20-25% of a person's nightly sleep |  
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        Term 
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        Definition 
        
        | condition in which the body is in a decreased state of activity, with the consequent feeling of being refreshed |  
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        Term 
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        Definition 
        
        | a condition in which patients are unable to lie still and report experiencing unpleasant creeping or tingling sensations in the legs |  
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        Term 
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        Definition 
        
        | state of altered consciousness throughout which varying degrees of stimuli preclude wakefulness |  
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        Term 
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        Definition 
        
        | passage through the four stages of NREM, then reversal and finally, entering REM sleep and returning the NREM Stage II |  
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        Term 
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        Definition 
        
        | a decrease in the amount, consistency and quality of sleep; results from decreased REM or NREM sleep |  
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        Definition 
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