The framework
Sleep alternates NREM ↔ REM in ~90‑minute cycles. NREM: N1 (transitional), N2 (spindles, K‑complexes), N3 (slow‑wave/delta, deepest, dominant early night). REM: desynchronised EEG, rapid eye movements, dreaming, and skeletal muscle atonia (dominant late night). Brain active, body paralysed.
Why architecture is diagnostic
- N3/deep NREM → disorders of arousal (sleepwalking, sleep terrors, confusional arousals) — early night, amnesic.
- REM → nightmares and REM sleep behaviour disorder (loss of atonia → dream enactment; a prodrome of α‑synucleinopathies).
- REM intrusion → narcolepsy phenomena (cataplexy, sleep paralysis, hypnagogic hallucinations).
- Depression classically shows reduced REM latency; alcohol/benzodiazepines suppress REM/N3 (and rebound on withdrawal).
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The reasoning habit
For any sleep complaint, ask: what's happening to REM, NREM, muscle tone, and arousal — and at what point in the night?
Pitfalls
- Treating "insomnia" generically without localising to a state/mechanism.
Pearls
- 🎯 Deep NREM (early) = arousal parasomnias; REM (late) = nightmares/RBD.
- 🩺 Timing within the night is a free diagnostic clue.
Next → The abnormal behaviours of sleep (Concept 37).