Understanding Sleep Cycles
Learn about sleep cycles, stages of sleep, and how they affect your overall health and wellbeing.
How sleep cycles work
What's a sleep cycle?
Every night your brain runs through the same pattern: light sleep, deep sleep, REM, repeat. One loop takes about 90 minutes. You do this 4 to 6 times before your alarm goes off.
The reason this matters is timing. Get woken up mid-cycle (especially during deep sleep) and you'll feel like you barely slept. Get woken up between cycles and you'll feel surprisingly fine, even on less total sleep.
The four stages
- 1
Stage 1 (N1) - Drifting off
That half-awake, half-asleep zone. Lasts 5-10 minutes. Someone slamming a door will snap you right out of it.
- 2
Stage 2 (N2) - Light sleep
Your heart rate slows and body temp drops. You spend about half the night here.
- 3
Stage 3 (N3) - Deep sleep
The repair stage. Your body fixes tissue, builds muscle, and boosts your immune system. Very hard to wake someone up from this.
- 4
REM sleep
This is where dreams happen. Your brain is processing memories and consolidating what you learned during the day. Your eyes move rapidly but your body is essentially paralyzed.
What a night looks like
A typical night's sleep, showing how you cycle through the stages. Notice how deep sleep happens more in the first half and REM increases toward morning.
Recommended Sleep Duration
- Newborns (0-3 months): 14-17 hours
- Infants (4-11 months): 12-15 hours
- Toddlers (1-2 years): 11-14 hours
- Preschoolers (3-5 years): 10-13 hours
- School Age (6-13 years): 9-11 hours
- Teenagers (14-17 years): 8-10 hours
- Adults (18-64 years): 7-9 hours
- Older Adults (65+ years): 7-8 hours
How to work with your cycles
- Same bedtime every night, weekends included (yes, really)
- Have a wind-down routine so your brain gets the hint
- No caffeine after 2 PM, and go easy on the alcohol
- Cool bedroom, dark room, minimal noise
- Screens off at least an hour before you want to be asleep
- Exercise during the day, but not within 3 hours of bedtime