Deepening

Fresh concept

The concept of deepening and vital depth is relatively new, despite having been observed for a very long time. As such, information on it is sparse and this article is not based on very much actual science (though the concept of shallower/deeper SWS is prominent in sleep science) - it consists mainly of information derived through anecdotal evidence and may change in the future.

Deepening is a part of adaptation, happening almost exclusively in stage-3. It is the process where vitals become deeper, meaning the same amount of vital sleep (REM and SWS) can now recover more of the respective pressure.

Feeling

The amount of vitals recovered in a sleep can be assessed by how long the sleep felt subjectively, but this does not distinguish between ls-compression and deepening, which both have this effect on perceived length. With sufficient ls-compression and deepening, a nap may end up feeling like several hours have passed, which is often the case for dawn naps (due to the REM peak).

Mechanism and occurrence

NREM sleep is on a continuum between NREM1 (transitional light-sleep) and NREM3 (SWS), with NREM2 in the middle. NREM2, when deepened, becomes NREM3, and as such, it makes sense for NREM3 to be able to deepen even further. Similar effects have been observed for REM, where many sleepers have reported differences between "shallow" and "deep" REM, where deep REM would recover more pressure.

The effect of deepening can be observed especially on extreme schedules (coreless, M3 and up, etc), where the vital baseline can no longer be met time-wise, but one may still be able to adapt because the vitals themselves become more efficient, without increasing in time. As a result, the vital baseline of the sleeper may shrink, and this effect can even last for a while after going back to mono, which results in a decrease in observed baseline TST. The effect rarely lasts long during recovery though, and as such, most go back to their natural baseline after a while.

Individuality

It is highly likely that, as with most other factors, deepening potential varies from sleeper to sleeper, contributing to the individual differences in what schedules can be adapted to. Unlike with ls-compression and internal repartitioning, deepening seems to only occur very selectively unless forced, and as such, an accurate prediction is likely not possible. As such, attempting an extreme schedule is likely the only way to know for sure if you can do it or not.