Sleep Architecture and Why Quality Matters as Much as Quantity Sleep is not a uniform state โ€” it cycles through distinct stages: N1 (light sleep), N2 (sleep spindles, memory consolidation), N3 (slow-wave deep sleep, growth hormone release, immune function), and REM (dreaming, emotional processing). A healthy 8-hour night completes approximately 5 cycles, each lasting 90-110 minutes. The hormonal events during each stage are specific and cannot be compensated for by longer sleep of poor quality. Growth hormone is released almost exclusively during N3 deep sleep, in pulses concentrated in the โ€ฆ