This is a bit like what Rabbi Krohn suggested. As we go through our days, we build up not only unwanted memories of inconsequential events and information, but also thoughts, words and actions that are better left in the past. Just as sleep washes away the thoughts and memories that deserve to be left in the past on a neurological level, spiritually too sleep is needed to push the past into the past, so that we can move on with what is worth saving to a new day, unencumbered by yesterday's failings.this was my comment over there:
Sleep is death, and it's bitul.. even if we can't reach bitul during the day, we get to taste it at night.. so it will give us an example for living..The questions were still rolling in my head and I happened to meet Rav Yisrael Avihai of Bet El in the Old City of Yerushalayim and asked him to clarify a little.
In the beginning of Likkutei Halachot, the halachot of waking in the morning and washing hands, Rebbe Natan discusses sleep a lot.
I have a post here that sums up some of what he says. (I also happened to relate it to science, a little) From that post I actually linked a few related posts to it..
Like how the Noam Elimelech says that HaShem sleeps down here in this world.
Also my favorite midrash is relevant here: When HaShem created Adam HaRishon, the Malachim couldn't tell him apart from HaShem and so they didn't know who to praise. It was only when HaShem made Adam HaRishon fall asleep (vayipol alav tardaymah) that the Malachim recognized HaShem.
The midrash was meant to teach the level of Tzelem Elokim.. so sleep is somehow what differentiates the Tzelem from the Elokim ..
also interesting, that there has to be more to sleep than just that it's a taste of death (or the death of yesterday or a death of the old self), because Adam HaRishon had not yet sinned and there was no death yet in the world, and still he slept!?! Was the creation of Chava a lowering of the level of the world? (ie. a form of death)
Death, in hassidut and kabbalah is defined as a fall in one's level.
I don't know if sleep falls into the same definition
Specifically I asked him about the relationship between death and sleep and how is it that there was sleep before there was death in the world?
He explained that sleep brings with it the potential toward a powerful aliyah. When it is practiced properly [just like everything else in life] then there is very great potential in sleep to rise to new and greater levels. [In fact, during sleep the Neshama can ascend to the heavens where it learns Torah.] In this sense, it can be said to be the opposite of death. Since any yeridah, any fall, is called by the name 'death.'
He also confirmed that the creation of Chava was a rise in the level of the world, and not a fall. (Hence Adam was put to sleep in order to reach this new level.)
More practically he clarified that "tasting death in sleep" is broken down like so: Chazal say that anyone who sleeps for 'sixty breaths' is said to taste death. [presumably meaning their sleep bears with it an aspect of death --- a fall and not just an aliyah] As to how long is 'sixty breaths' some hold that it is a half hour, some hold an hour, some hold six. In practice, the Arizal said that any sleep [from the start of the night until] before midnight doesn't count as 'sixty breaths' so if you get all your sleep in during the first half of the night, you aren't tasting death.