A night of sleep comprises 4 to 6 cycles through sleep stages and each cycle is around 90 minutes.

TODO: hypnograms

REM Sleep

Rapid eye movement sleep (REM) Dreaming usually occurs during REM Muscles paralysed Time in REM sleep increases through the night (25% of total sleep time)

NREM Stages

  • stage 1: Transition between wake and sleep. Easy to wake from, may not be aware asleep (5% of total sleep time)
  • stage 2: Light sleep (45%)
  • stage 3 - previously devided into stage 3 and 4: also known as slow-wave sleep (SWS), deep sleep, harder to wake from. Results in “sleep inertia” if woken from this stage (25%)

References