1# Why We Sleep: Key Findings
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3Sleep is the single most effective thing we can do to reset our brain and body.
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5## Sleep Architecture
6- NREM Stage 3 (deep sleep): physical restoration, immune function
7- REM: emotional processing, creativity, memory consolidation
8- Each cycle ~90 min, 4-5 cycles per night ideal
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10## The Cost of Sleep Debt
11- After 1 week of 6h/night: cognitive performance equals 0.05% BAC
12- Chronic sleep debt linked to Alzheimer's — glymphatic clearance drops 60%
13- 5h sleep → testosterone drops 10–15% in healthy young men
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15## Practical Sleep Hygiene
16- Optimal bedroom temperature: 18–19°C
17- No blue light 90 min before bed — melanopsin sensitivity peaks at 480nm
18- Caffeine half-life 6h: last intake before 2pm
19- Wake-time consistency matters more than bedtime consistency
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21## Open Questions
22- Do naps compensate for night debt? Evidence mixed
23- Melatonin: 0.3mg as effective as 3mg. Most supplements are overdosed.