One cannot prove positively that consciousness(soul) has vanished in sleep. One can only show it negatively. For one cannot know the limits of consciousness(soul): one cannot posit where it starts, stops, vanishes etc. This is what intellectuals do not understand. The word consciousness includes non-dual states like sleep, whereas intellectuals use it only for states of duality(waking/dream). Intellectuals do not grasp that consciousness can remain without objects, as in sleep, and yet be conscious still; this is "content -less or experience -less consciousness."
Dream shows that a second object can be present (duality) and yet one know later it was not really so. Similarly in waking one’s sense of duality is a delusion.
They object that there is nothing in deep sleep. The term nothing indicates the existence of a thing to start with, therefore non-existence implies existence. Nothing must have a meaning, i.e. an experience and if one had not seen there was a waking world he could not negate it in sleep. Waking and sleep go together; one is not possible without the other.
One gets deep sleep even in the waking experience. It comes during interval between two experiences, when one goes and the other appears. Hence non-existence of consciousness in deep sleep is wrong. It is like the waves disappearing but their substance or essence, water, remains.
Because one is not aware of any other things in deep sleep, he has to admit that every idea both internal and external has merged into the soul during sleep as undifferentiated consciousness.
Dream also is a waking experience to the dreamer. When one gets up he has another waking experience. Strictly speaking, he has a succession of "waking experiences."
The illusions of dream disappear when waking takes place then they are seen to be unreal. Similarly the illusions of waking also disappear when the non dual wisdom dawns and it is seen as equally unreal. The objects, persons, and talks of both experiences are all illusion. The next step is to know the nature of all these experiences are only the mental. All names and forms are imaginary, but Atman(soul) the true self always there, whether one sees them or not.
One imagines the waking world and then imagines the dream world and then proceeds to find the former as the cause of the latter. This is mere delusion. Dream experience also appeared spontaneously, same way as waking experience.
Those few who never dream cannot apply the spiritualistic analogous to it, nor the Gnani-test of feeling himself the All in dream! However this does not matter, for they can still apply the latter test to waking only but they are unfortunate in missing the former illustration; this will not prevent realization through.
The three states come and go, impermanent and therefore have no value from the standpoint of the formless witness, all yogic visions and astral travel likewise come and go, and are valueless.
They are but illusion, as the light seen by yogis and mystics, and the astral world experience quite genuine but of no value on the standpoint of truth.
