Glossary of Sleep-related terms

NREM-REM Sleep Cycle (synonymous with Sleep Cycle)

A period during sleep composed of a NREM sleep episode followed by a REM sleep episode. Each NREM-REM sleep couplet is equal to one cycle; with the average duration in adults being 90 minutes. An adult sleep period of 6.5-8.5 hours generally consists of four to six cycles.1