What are the different sleep stages?

Sleep is categorized into two major types:

• NREM (Non-Rapid Eye Movement) → 3 stages
• REM (Rapid Eye Movement) → 1 stage

1. NREM Stage 1 (Light Sleep)

• Duration: ~5–10% of total sleep
• What happens:
  • Transition from wakefulness to sleep.
  • Muscles relax, heart rate slows slightly.
  • Lightest sleep stage; easy to wake.
• Brain Activity: Theta waves.
• Typical Time in Night: At the start of the night, during the first few minutes of each cycle.

2. NREM Stage 2 (Light Sleep)

• Duration: ~40–50% of total sleep (largest share)
• What happens:
  • Heart rate slows, body temp drops.
  • Reduced awareness of surroundings.
  • Sleep spindles and K-complexes appear (brain wave patterns).
• Purpose:
  • Memory consolidation begins.
  • Body relaxes more deeply.

3. NREM Stage 3 (Deep Sleep)

• Duration: ~20–25% of total sleep (more early in the night)
• What happens:
  • Slow delta brain waves dominate.
  • Very difficult to wake up.
  • Growth hormone released; physical repair and recovery occur.
• Benefits:
  • Tissue repair, immune function, growth.
  • Energy restoration.

4. REM Sleep

• Duration: ~20–25% of total sleep (more later in the night)
• What happens:
  • Rapid Eye Movements.
  • Brain highly active (similar to wake state).
  • Vivid dreaming occurs.
  • Muscles paralyzed (atonia) except eyes and breathing muscles.
• Benefits:
  • Emotional regulation.
  • Learning and memory (especially creative/problem-solving).

Sleep Cycle Pattern

• A typical cycle:
  Stage 1 → Stage 2 → Stage 3 → REM → repeat
• First half of the night: more deep sleep (Stage 3).
• Second half: more REM sleep.

Healthy Adult Sleep Breakdown (8 hours)