What Is REM Sleep?
REM (rapid eye movement) sleep is a sleep stage characterized by rapid eye movements, vivid dreaming, and temporary relaxation of most muscles. In healthy adults it typically makes up about 20% to 25% of total sleep, occurring in longer periods later in the night.
REM vs. Deep Sleep
Deep (slow-wave) sleep is concentrated earlier in the night; REM periods lengthen in later sleep cycles.
Sleep Stages
A typical night cycles through light sleep (N1 and N2), deep sleep (N3), and REM sleep several times. Sleep trackers estimate stages from movement and heart rate, while sleep laboratories measure them with brain-wave recordings (polysomnography).
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🔗 Related Terms
More Health & Fitness Terms
- Basal Metabolic Rate (BMR)
- Body Composition
- Body Fat Percentage
- Body Mass Index (BMI)
- Calorie
- Calorie Deficit
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Last updated: September 27, 2026. This definition is for general educational purposes only. It is not financial, investment, tax, legal, or medical advice, and it does not recommend any product or course of action. For decisions about your own situation, consult a qualified professional.