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2009 ICD-9-CM
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| Sleep Stages Drowsiness | Lethargy | Drowsinesses | Lethargies | Sleep Stage | Stage, Sleep | Stages, Sleep Periods of sleep manifested by changes in EEG activity and certain behavioral correlates; includes Stage 1: sleep onset, drowsy sleep; Stage 2: light sleep; Stages 3 and 4: delta sleep, light sleep, deep sleep, telencephalic sleep. |