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sleep stage 2

A stage of non-REM sleep characterized by the presence of sleep spindles and K complexes present in a relatively low-voltage, mixed-frequency EEG background; high voltage delta waves may make up to 20% of stage 2 epochs; usually accounts for 45-55% of the major sleep episode.

Definition reprinted with permission from Culebras, Antonio, Clinical Handbook of Sleep Disorders, Butterworth-Heinemann