Sleep occurs in cycles that move through different stages, each with unique brain activity and functions. These stages fall into two main types: NREM (non-rapid eye movement) and REM (rapid eye movement) sleep.
💤 The 4 Stages of Sleep:
Stage 1 – Light Sleep (NREM 1)
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Duration: 1–7 minutes
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Lightest stage of sleep
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You drift in and out; may experience muscle twitches or the feeling of falling
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Brain waves begin to slow
Stage 2 – Deeper Light Sleep (NREM 2)
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Duration: 10–25 minutes (and lengthens in later cycles)
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Heart rate slows, body temperature drops
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Brain waves slow with brief bursts of activity (sleep spindles)
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You’re harder to wake than in stage 1
Stage 3 – Deep Sleep (NREM 3)
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Duration: 20–40 minutes (more in early sleep cycles)
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Also called slow-wave sleep or delta sleep
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Body repairs tissues, boosts immune function, and builds bone/muscle
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Very difficult to wake up; grogginess likely if disturbed
Stage 4 – REM Sleep (Rapid Eye Movement)
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Begins ~90 minutes after falling asleep
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Brain activity increases—similar to wakefulness
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Most vivid dreams occur here
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Body is paralyzed (to prevent acting out dreams)
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Crucial for memory, learning, and emotional processing
🔁 The Sleep Cycle
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One full cycle lasts about 90–110 minutes
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You go through 4–6 cycles per night
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Early in the night = more deep sleep
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Later in the night = more REM sleep
Why It Matters:
Each stage plays a unique role in your physical and mental health:
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Stage 3 restores your body
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REM sharpens your mind and mood
Disruptions (like stress, noise, or poor sleep hygiene) can throw off this balance and leave you feeling tired—even after “enough” hours of sleep.