Sleep & Recovery

Learn what metrics like sleep score, REM percentage, and heart rate variability represent on a typical consumer sleep tracker, and which figures deserve attention versus which are noise. The article explains the calculation methods behind these numbers and their known margins of error.

This explainer defines sleep debt as an accumulated shortfall of sleep hours and distinguishes it from chronic fatigue, a persistent tiredness that does not resolve with extra sleep. It outlines the practical markers that separate the two conditions.