Sleep stages naturally vary between nights. The Ohayon et al. meta-analysis summarizes normative sleep-stage values in healthy populations and provides context for interpreting REM observations.
Because stage estimates depend on the device and the sleep period captured, Yuelu uses them as one signal among several. A value outside a population summary does not by itself indicate a health problem.
Original source
Ohayon et al., Sleep (2004), “Meta-analysis of quantitative sleep parameters from childhood to old age in healthy individuals.” Read the PubMed record.
Interpretation note
Use repeated trends, personal baseline, symptoms, and professional assessment together when a change persists or causes concern.