Polysomnograms of most homeothermic species distinguish two states, Rapid Eye Movement (REM) Sleep and Non-Rapid Eye Movement (NREM) Sleep. These alternate several times during the night, for reasons and following rules that remain poorly understood. It is unknown if each state has its own function and regulation or whether they represent two facets of the same process. The present study compared the mean REM/NREM sleep ratio and the mean Number of NREM-REM sleep Cycles across three consecutive nights. The rationale was that if REM sleep and NREM sleep are tightly associated, their ratio should be comparable whatever the cycle frequency in the night. Twenty-six healthy subjects of both sexes were recorded at their home for four consecutive nights. The correlation between the REM/NREM sleep ratio and the Number of Cycles was highly significant. Of the two sleep components, REM sleep was associated to the Number of Cycles, whereas NREM sleep was not. This suggests that the relationship between REM sleep and NREM sleep is rather weak within the cycles, does not support the concept of NREM-REM sleep cycles as miniature units of the sleep process, and favors the concept of distinct mechanisms of regulation for the two components.