I was reading about Stage 3 is the phase that likely is where "restorative" emerges...and that deepest sleep state is also when the brain waste flushing takes place/brain cleaning.
https://www.sleepfoundation.org/stages-of-sleep
reading below- sounds like a promising stage for our sleep to be a mess.
Stage 3 / N3
Stage 3 sleep is also known as deep sleep, and it is harder to wake someone up if they are in this phase. Muscle tone, pulse, and breathing rate decrease in N3 sleep as the body relaxes even further.
The brain activity during this period has an identifiable pattern of what are known as delta waves. For this reason, stage 3 may also be called delta sleep or slow-wave sleep (SWS).
Experts believe that this stage is critical to restorative sleep, allowing for bodily recovery and growth. It may also bolster the immune system and other key bodily processes. Even though brain activity is reduced, there is evidence that deep sleep contributes to
insightful thinking6,
creativity7, and memory.
We spend the most time in deep sleep during the first half of the night. During the early sleep cycles, N3 stages commonly last for 20-40 minutes. As you continue sleeping, these stages get shorter, and more time gets spent in REM sleep instead.