Only the knowledge of this non-difference can bring unity in diversity

Deep sleep is unconscious self-awareness. It is unconscious self-awareness because one becomes aware of the deep sleep experience only when waking takes place. The waking experience is the state of ignorance.  Everything exists in deep sleep but the innermost  self  remains  in its own true nature.  The waking or dream(mind or universe) rises form deep sleep and subsides as deep sleep.  Whole waking or dream. 

All the phases of the ego's dualistic thoughts and feelings and sensations within the waking or dream have their origin in deep sleep; they come from there and they disappear there.

Deep sleep as the cause of our individual life is inferred, not seen. However beyond deep sleep is the Atman. This deep sleep as source is equivalent to "The Unconscious" of the psycho-analysis. 

A quarter of a dollar  is included in a one-dollar bill; a half dollar is already there in one dollar. Therefore the quarter and half dollar are merged in the one dollar bill: when one has a whole dollar he doesn’t inquire, does it contain a quarter or half dollar in it: he knows that both are present therein. You can by inquiry convert, merge or dissolve all the parts of a dollar in the whole one. Similarly one can show that waking dissolves in dream, the dream disappears as deep sleep, and latter merges in Atman. This is done by converting objective world into an experience. In the beginning the seeker has to learn first quarter, half and whole and he has to learn the fact that the stuff that becomes of these dual and non dual experiences is Atman. 

Conscious deep sleep is called Samadhi. Conscious dream is called visions, mind-made by yogis.  The conscious awareness of   the formless substance and witness of the three states is non dual wisdom.

The difference between deep sleep and Nirvana  is the nature of the formless  soul, the innermost self.   The ego is still latent in the former state, whereas there is neither latent ego nor latent intellect in the state of Nirvana. Intellect cannot function in Nirvana and therefore cannot tell one anything about it.

A further difference between the dual and non dual experiences is the presence of consciousness in the fourth. Nothing can be understood unless it is distinguished or differentiated from something else. For this reason, deep sleep, which offers no contrasts and no differentiations, cannot be known in the ordinary sense. The contrast gives one the ability to observe the reality. Unless one examines the nature of the mind and realizes the fact that the mind is duality and the formless clay of the mind is non dual in its nature.  

Of what stuff the waking or dream is made? In the dream it is the same stuff as the seer/ witness; hence in the case of dream one can easily see the real unity in apparent duality. So also in waking experience for the time being one does not know that the waking is of the same stuff as the Atman: although the world appears different it is nevertheless non-different when inquired into. 

Only the knowledge of this non-difference can bring unity in diversity. The lion and the tigers have the strongest sense of separateness and hence prey on other animals. "Illusion” really means one does not know that the waking or dream is made of the same stuff as the true Self, which is Atman. 

Just as one knows of dream only on waking inquiry similarly he knows of reality only through deeper self-search: and just as the dream disappears waking takes place, through  soul-centric reasoning, the ignorance disappears, and  one realize the form,time and space are mere illusion created out of consciousness.