For the 'scientific' explanation, first read:
This strange-seeming way of thinking about dreaming, the awake state and deep sleep comes from combining the Mormon understanding that we had a pre-mortal existence with an insight of William Arkle that our mortal, earthly incarnated life is characterized by being a slowly-moving, close-up and detailed form of consciousness as perceived from a 'Heavenly' perspective.
This is related to trying to understand the reason for earthly incarnated mortal life - what is it that we can do in this form of existence that could not be accomplished in Heaven/ an immortal and spiritual world (or, at least, would be more difficult, slower, less probable than in Heaven).
I am also trying to understand how - say - angels can operate between Heaven (or some other spiritual realm) and Earth - how they can sometimes apparently get so much done in such a short period of time; yet at other times are described as taking-on bodies and operating on a human timescale, but somewhat like 'superhuman' Men.
Anyway, I came-up with the idea that from the awake perspective we have an understanding of Heavenly operations in dreaming sleep - when there is so much done in a very short time.
So Heavenly time and action can be understood as a more extreme version of the dreaming mind as it is perceived by our awake mind; in the sense that we can experience (say) a thousand hours of dreaming experience in just one hour of awake time - or can accomplish things a thousand times faster while dreaming than while awake.
And, alternatively from the perspective of our awake state, we could view deep sleep as analogous to how earthly, mortal incarnate life might seem to a Heavenly being such as an angel. Our earthly mortal incarnate life might seem incredible slowed-up and uneventful.
When we awaken from deep sleep, it seems as if little or nothing has been going on - perhaps just a certain mood, or theme remains... Likewise, an angel might have time to think and do a thousand things while we were only able to think a sentence, lift a hand or experience a mood.
And, perhaps, to angelic consciousness a whole human lifespan seems like the life of a mayfly...
This would mean that human consciousness perceives vastly more detail, drama, dilemmas per unit time than do angels - all the great issues of which we are aware in mortal life may just whiz past an angelic consciousness.
So mortal incarnate life on Earth might be much better that the Heavenly realm as an arena for the exercise of human agency, free will, as a place when the choices arrive slowly, singly, linearly - where the whizzing pace of spiritual existence gets slowed-down, dissected into its components, put under a microscope...
I find this helpful in understanding why it was necessary (or most-beneficial) to create an earth for men to be born into as mortals - why this situation is better than Heaven for doing what we are here to do.