Unstable adaptation

It is possible that the adapted state is unstable or gets destabilized for a sleeper. Some events, injuries or substances can throw off the sleeper from being adapted in most cases. There are a few types of sleep destabilization or generally unstable adapted state, which are described below.

Low total sleep time

It is usually very difficult to adapt to schedules with a low total sleep time, since much more sleep compression should occur, leaving significantly much less light sleep. This makes the sleep schedule much less flexible and generally unstable, because any event or substance, which temporarily increases sleep needed, can easily compromise adapted state. This is likely the main reason why long term polyphasic sleepers more often are those, who stay on a schedule, which reduces little-to-no sleep, while most nap-only adaptations are shorter.

Also, schedules, which reduce much sleep, require much denser blocks of sleep during the day because of the wake time reduction, so shorter wake gaps are possible, which makes such schedules inconvenient for daily life and thus unstable long term.

Increased sleep needs

Sleep needs can be increased temporarily, usually as an effect of needed physical recovery. Such cases include increased physical activity, some substances, such as cannabis or alcohol. External impact sometimes can significantly increase sleep needed, mostly SWS, which can shake the adapted state, again depending on the total sleep time of the schedule. This is the main reason why schedules with at least 3 sleep cycles are commonly recommended in the polyphasic community for those with intense physical activity, to guarantee the possibility to accomodate enough SWS in core(-s).

In some cases, REM sleep can be increased as well, this includes depression or possibly intense mental activity.

Flexing

Polyphasic sleep schedules usually become flexible after adaptation. The possible level of flexing depends on the scheduled total sleep time and on the stability of adaptation. The sleep schedules, which reduce much sleep, generally are much less flexible than the ones with higher total sleep time, as flexing is known to decrease sleep quality, which is unacceptable for the schedules with extreme compression. When sleep is flexed too much, the adaptation can be destabilized or even ruined, as the compression can't be maintained anymore.

Also, the adaptation to flexing should be done gradually by incresing the flexing range slowly after the sleeper is already adapted and the sleep is stabilized. By flexing too much and being too fast, it is likely to destabilize adaptation as well, which happened to some members of the polyphasic discord community.