On Mandukya 5-6: This [prajna, undiferentiated consciousness of deep sleep] is the Lord of all [Sarvesvara, Isvara, Saguna Brahman].

He who has got this state of deep sleep as his sphere is su,cupta- sthanah. He is said to be ekibhutah, undifferentiated, since the whole host of duality, that are diversified as the two states (of waking and dream) and are but modifications of the mind, become non-discernible (in that state) without losing their aforesaid characteristics, teristics, just as the day together with the phenomenal world becomes non-discernible under the cover of nocturnal darkness. As such, conscious experiences, that are but vibrations of the mind in the waking and dream states, become solidified, as it were. This state is called prajnanaghanah, a mass of consciousness, since it is characterized by the absence of discrimination. It is a mass of mere consciousness like everything appearing pearing as a mass by becoming indistinguishable under nocturnal darkness. From the use of the word eva, merely, it follows that there is nothing of a separate ate class other than consciousness. And he is dnanda- mayah, full of joy, his abundance of joy being caused by the absence of the misery involved in the effort of the mind vibrating as the objects and their experiencer; encer; but he is not Bliss itself, since the joy is not absolute. Just as in common parlance, one remaining free from effort is said to be happy or dnandabhuk, an experiencer of joy, so this one, too, is called dnanda- bhuk, for by him is enjoyed this state that consists in extreme freedom from effort, in accordance with the Vedic text, `this is its supreme bliss' (Br. IV. iii. 32). He is cetomukhah, since he is the doorway to the consciousness sciousness of the experiences in the dream and waking states. Or he is called cetomukhah, because consciousness, ness, appearing as empirical experience, is his doorway or entrance leading to the states of dream and waking. He is called prdjnah, Prajna, conscious par excellence, since in him alone is there the knowledge of the past and the future and of all things. Even though lying in deep sleep he is called Prajiia (conscious) because of his having been so earlier (in the two former states of dream and waking) ; or he is called conscious, since he alone is possessed of the peculiar characteristics of mere (undiversified) consciousness, whereas the other two have diversified knowledge as well. This Prajiia, as described, is the third quarter.

~Shankara on Mandukya 5 [on deep sleep] (tr-Gambhirananda)

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All three states have a common feature, namely, the absence of the Knowledge of Reality. But deep sleep differs from waking and dreaming in that it is associated neither with gross objects nor with subtle impressions, which are the characteristics of the other two.

Deep sleep is a state of ease and repose. The friction caused by the subject-object relationship is absent. Hence a person in deep sleep experiences bliss, in the sense that one who is free from effort is said to be happy. This bliss is quite different from that of Brahman.

The unified consciousness of deep sleep, wherein all diversities disappear, is the antecedent of the waking and dream experiences. Hence it is regarded as the cause of, or the door to, the other two states.

~Nikhilananda on Mandukya 5

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This [prajna, undiferentiated consciousness of deep sleep] is the Lord of all [Sarvesvara, Isvara, Saguna Brahman], this is the knower of all [jnana], this is the inner controller [of Maya], this is the source of all [manifestation]. And this is that from which all things originate and in which they finally dissolve themselves. [Brahma, Vishnu, Shiva]

~Mandukya 6 (tr-Chinmayananda) [notes in brackets are mine]