From Polyphasic Sleep Wiki

Sleep-onset SWS, or SOSWS, is a phenomenon in which slow-wave-sleep onset latency is greatly reduced, wherein an individual transitions rapidly from wakefulness to SWS, shortening the period of light sleep that normally characterizes the beginning of the sleep cycle.


After a sustained period of sleep deprivation, especially of SWS, SWS becomes prioritised by the body and its onset latency greatly reduces.[1] Similarly to sleep-onset REM[2], SWS latency can reduce to less than 10 to 15 minutes.

Application to polyphasic sleep

Most polyphasic sleep schedules, which contain at least 3 full sleep cycles in core(s), rarely cause significant SWS loss. SOSWS is more common for extreme schedules, such as the nap-only schedule line. This mechanism causes entering SWS almost immediately, which produces SWS-filled naps on these schedules. Under such circumstances, these naps can become extremely difficult to wake up from, even more so then REM-filled naps after REM rebound. This represents one of the main obstacles in adapting to a nap-only schedule.


  1. Ferrara M, De Gennaro L, Bertini M (1999). "Selective slow-wave sleep (SWS) deprivation and SWS rebound: do we need a fixed SWS amount per night". Sleep research online. 2 (1): 15–19.
  2. American Academy of Sleep Medicine. Central disorders of hypersomnolence. In: The International Classification of Sleep Disorders – Third Edition (ICSD-3) Online Version. Darien, IL: American Academy of Sleep Medicine; 2014