In terms of our subjective experience of Time, there is a gradient between the three conscious states - Deep sleep, Waking and Dreaming, between-which we alternate through our lives.
Deep sleep - when we are hardly aware of Time passing, and hardly anything seems to be experienced (in so far as we recall anything at all from Deep Sleep - I personally do not).
Waking - when Time passes in the way we know; not always at the same subjective speed, but within limits of a few-fold variation between time passing quickly and slowly. Experience likewise.
Dreaming sleep - in which time seems to pass at the same subjective speed as it does in waking life, but, relative to waking life Dreaming sleep moves much more rapidly; so that we can fit ?100 fold more events and emotions into a section of dreaming, than we could do in the equivalent time awake.
In other words, Dreaming is a very rapid and complex type of cognitive processing. However, Dreaming is poorly remembered; and notoriously unreliable - in terms of its content being incoherent within itself, and incoherent with subsequent and previous experience.
This implies that the gain in rapidity and complexity of mental processing that we get in dreaming has a price to pay in terms of the validity of 'conclusions'.
We can think, and experience, many many more things in five waking-minutes of a dream than in five waking-minutes; but a great deal of the dream material is unreliable, and does not stand up to scrutiny: it is not confirmed by experience.
If we assume that these conscious states are on a continuum; then I can back-extrapolate to the situation of Deep sleep. I can then assume that:
1. Deep sleep is necessary - and has important functions; or else we wouldn't do it, and would not have to do it.
2. Deep sleep is only capable of very slow and simple cognitive processing.
3. The thinking of Deep sleep is of the greatest coherence, within itself and with Life; and the knowledge of Deep sleep has the highest validity.
In sum, Deep sleep seems to be a kind of Intuition. That is; a bottom-line form of thinking, a self-validating form of thinking. If we can Deep sleep a thing; then that thing is real: or, it is as subjectively-real as something can be, for us.
My guess is that the things were are most sure about, or become surest about; are things that we have 'processed' in Deep sleep; and that the slowness, and simplicity of concepts, of Deep sleep is a constraint upon our capacity really to know things.
Note, aside: I've hidden the blog comments for a while, to take a break from dealing with them. I shall reveal them again soon, when I feel refreshed.