The Upanishad has spoken of the deep sleep state at length.+

It is erroneous to judge and reason the Advaitic truth from the dualistic perspective. Advaitic truth is the soulcentric truth, whereas dualistic truth is egocentric.  The ego (you) is the false self within the false experience (duality). The Soul is the real Self.  Thus, whatever is based on the ego is bound to be a falsehood, and whatever is based on the soul is real and eternal. 

Every minute the waking experience is changing.  The waking experience becomes deep sleep and deep sleep becomes the dream. Thus, continuous change is going on and on in consciousness.  

The one which becomes waking, that one that becomes a dream and that becomes the deep sleep is the Soul, which is present in the form of consciousness. 

Thus, all three states are created out of single stuff and that stuff is consciousness.  Thus, one, which becomes the duality (waking or dream) and the one which becomes the nonduality (deep sleep) is the same consciousness. Thus, consciousness alone is real and all three states are merely an illusion. 

The ego is present only in the waking or dream. The dream ego is limited to the dream. Similarly, the waking ego is limited to the waking experience alone.  The ego, body, and the world of the dream appear together and disappear together. Similarly, the ego, body, and the world of the waking experience appear together and disappear together. 

 The Self is neither the dream entity nor the Self is the waking entity (you) but the Self is the  Soul, which witnesses the coming and going of the three states.   The Soul, the   Self is nothing to do with the three states because it is not an entity or identity within the three states. 

Sage Goudpada: ~ To establish the truth of Non-duality by sheer reasoning alone. He begins by defining "What is real?" "What is unreal?" etc, because that is the right way to discuss or teach. People must first know what they are talking about. (Mandukya Karika)

How does one see various objects, scenes, and persons during dreams? If the dream is experienced without the physical body, then what is it that experiences the dream? Therefore, there must be a formless witness of the dream world. This formless witness is the same witness that is witnessed this Waking experience also. Therefore the Waking experience and dream both are witnessed by one and only formless witness of which the seeker is not aware. Since he considers the physical body (I) as the self or witness and views and judges the world-view from the standpoint of the false self, within the false experience. The formless witness can exist with or without waking or dream. But the waking/dream ceases to exist, without the formless witness.

The gross Waking experience is merged into the mental experience in the sense that, when it is analyzed, it is found to exist inseparably in and as the mind alone. All "spiritual" planes are really mental: those who regard them as different or higher are deceiving themselves. The dream becomes unreal when the waking takes place; similarly, the waking becomes unreal when the wisdom dawns. Therefore, everything has to be grasped mentally, not argued from an intellectual point of view, which is limited to the false physical entity within the false experience.

The waking experience is a state of ignorance. In the state of ignorance, the self (soul) remains to experience the illusion as a reality.  

Till illusion remains a reality, he will remain ignorant of the fact that the cycle of birth, life, and death is merely an illusion.  Therefore, it is not possible for one to accept the fact that the world is an illusion, till he becomes aware of the fact that, the Self is neither the waking entity nor the Self is dream entity but the Self the formless soul or consciousness, which is substance and witness of the three states.  Therefore, those who believe the waking entity as the Self, and refuse to accept the Soul as the Self and they think by getting rid of the ego or by surrendering to their Guru is the means to Self-realization. 

All three states and their substance and witness are one in essence. That essence is the soul, which is present in the form of consciousness (Spirit). Thus,  the experience of duality is made of single stuff. That single stuff is consciousness. That single stuff becomes many and many (duality) become the single stuff (non-duality). Thus,  it is necessary to realize what is it that becomes duality and what is it that becomes non-duality.

In the dream, the mountain which is apparently insentient and material is nevertheless still your mind alone. Whether living or dead, conscious or unconscious thought or matter; all things are appearances of one and the same consciousness. All these distinctions are seen by Gnani as only the consciousness. 

The look of an object will depend upon the medium through which the observer views it. In fact, our mental and intellectual conditions determine the three states, observed and experienced.  The commoner viewing the three states will see differently from a Gnani viewing the same three states. Each one interprets the three states that they see in terms of their existing knowledge. The commoner sees everything based on the ego, therefore, experiences birth, life, karma,  death, and the world as reality,  whereas a Gnani sees everything as consciousness and he is fully aware of the fact that, there is no second thing that exists other than consciousness.

The Sleep State:~

The Upanishad has spoken of the deep sleep state at length.  This has several purposes.

   1. To reiterate that the objective world does not have a permanent reality

   2. To demonstrate that the subject alone remains as the non-dual reality in the sleep state and therefore in all the states.

   3. To prove that the sleep state, being non-dual, gives the greatest bliss to the subject consciousness.

   4. To prove to the subject-enquirer that bliss is obtained not from objects but on the contrary, in the absence of objects.

   5. To prove that duality is samsara, misery and non-duality are liberations, and bliss.

   6. To give to the sAdhaka a? preview? a foretaste,  of the liberated state.

Brihadaranyaka Upanishad 4.3.22 alludes to this experience:-  (In this state a father is no father, a mother no mother, gods no gods, the Vedas no Vedas.  In this state, a thief is no thief, the killer of a noble brahmaNa no killer? a monk no monk, a hermit no hermit. This form of his is untouched by good work and untouched by evil work, for he is then beyond all the woes of his intellect.)

Sage Sankara says:  VC- How can the talk of diversity, dvaita (duality), apply to the Supreme Reality which is one and homogeneous, Advaita (Nonduality)? Who has ever observed diversity, dvaita, in the unmixed bliss of the state of profound sleep?

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Q:~ If one goes under anesthesia. Totally blank state. There’s no witness even.pls, explain. 

(“Dear Santthosh Kumaarji one doubt I have to get clarified, last week one of my friends go thru surgery. After the seduction injection what he experienced was nothingness .free from body and mind .and felt totally blank'.pls, explain that state. Is that state is the sushupthi?”)

 Santthosh Kumaar:~Suppose if you had asked the  same question to me in a dream: ~ 

 (“Dear Santthosh Kumaarji one doubt I have to get clarified, last week one of my friends go thru surgery. After the seduction injection what he experienced was nothingness .free from body and mind .and felt totally blank'.please explain that state. Is that state is the sushupthi?”)

 Suppose Anastasia is given in a dream then the dream becomes unreal when waking takes place. Similarly, the waking becomes unreal when wisdom dawns. The wisdom dawns when one realizes the existence of the witness of the three states. The soul is the witness of the coming and going of the three states.  From the standpoint of the soul, the three states are non-existent as reality. Thus, our individual experiences within the waking are as real as a dream. 

Sushupthi is still the state of ignorance because we become aware of the sushupthi in the waking experience. The waking experience is a state of ignorance.  Thus, just getting blankness is not self-awareness.

Self-awareness arises in the midst of waking when one realizes, that his body and his experience of the world (form, time, and space)   are made of single stuff. That single stuff is the soul, which is present in the form of consciousness.  Thus, realizing our body and our experience of the world are made out of single stuff leads to Advaitic self-awareness in the midst of diversity (duality).   

One has to imagine by holding the deep sleep state as the Soul, the Self, then view and judge the waking or dream just to realize there is no form, time and space have become one in essence in the state of deep sleep. That is,  there is no duality of any sort.:~Santthosh Kumaar