What sleep stage is worst to wake up from?
Waking from N3 slow-wave (deep) sleep generally produces the most sleep inertia, REM sleep is in between, and light N1/N2 sleep is the mildest, although not every study finds a sleep-stage effect.
The N3 problem
N3 is the deep, restorative phase. Abrupt awakening from it produces more inertia than awakening from stage N1 or N2 (Tassi & Muzet, 2000); in one nap study, people woken from slow-wave sleep performed 41% worse than before the nap (Hilditch & McHill, 2019).
REM is also rough
Waking from REM sleep produces an intermediate level of inertia, between deep and light sleep (Tassi & Muzet, 2000). You often wake in the middle of a dream.
Best wake stages
N1 or N2 light sleep produce the mildest inertia. 'Smart' alarms try to target these stages, though their accuracy is debated.
Sources
- Hilditch & McHill, Nature and Science of Sleep, 2019. Sleep inertia: current insights
- Tassi & Muzet, Sleep Medicine Reviews, 2000. Sleep inertia
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