REM Sleep

REM Sleep—rapid eye movement sleep—is a sleep stage characterized by high brain activity, rapid eye movements, vivid dreaming, and marked skeletal-muscle suppression. REM is associated with memory consolidation, emotional processing, and other forms of cognitive recovery. Garmin estimates REM from movement, heart rate, heart-rate variability, and related wearable signals. It does not measure brain waves directly, so Sleepgenic treats REM hours and REM percentage as consumer-wearable estimates rather than polysomnographic stage measurements. Zero-valued observations remain preserved when they are present in the source instead of being silently converted to missing values. REM episodes tend to become longer later in the sleep period, which means shortened or early-ended sleep can reduce the opportunity for later REM. Training load, travel, altitude, illness, stress, sleep timing, and device classification noise can also coincide with lower estimates. A single low-REM night does not identify the cause. In the Sleepgenic n=1 record, REM has sometimes weakened during demanding periods or diverged from headline scores. That makes it a useful longitudinal signal, not proof that REM is universally the first or most fragile stage under load. Canonical v1 evaluates REM duration, REM percentage, rolling personal baseline, and real-world context together.