13.1 Sleep Architecture: What Happens While You Sleep

A single night of sleep consists of 4–6 cycles, each approximately 90 minutes, cycling through:

The first half of the night is dominated by deep (NREM) sleep — critical for physical recovery. The second half is dominated by REM — critical for cognitive and emotional recovery.

Cutting sleep short by even 1–2 hours primarily eliminates the second REM cycles, impacting mood, cognitive function, and hormonal regulation the following day.

13.2 Circadian Rhythm Optimization

Light as the Master Zeitgeber

Sunlight in the morning (within 30–60 minutes of waking) is the single most powerful anchor of the circadian clock. Morning bright light:

• Triggers cortisol's healthy morning peak (alertness)
• Sets the adenosine and melatonin release timing for the evening
• Regulates serotonin and dopamine production throughout the day

Blue light at night (screens, LED lighting) suppresses melatonin onset by 1–3 hours, delays sleep initiation, and reduces deep sleep quality. Use warm-toned lighting after sunset; blue-light blocking glasses if screens are unavoidable.

Room Temperature

Core body temperature must drop ~1–1.5°C to initiate and sustain sleep. Optimal sleep environment: 16–19°C (60–67°F). A warm pre-sleep shower paradoxically aids sleep onset by drawing blood to the periphery and accelerating core temperature reduction.

Sleep Supplementation