“Now is described the world-bound nature of the Atman as well as its associations with the three states, which are possible only when the ego identifies itself with the body: –
10. In the state of deep sleep, when (the thought of) ego disappears[1] the body also becomes unconscious. The state in which there is the half manifestation of the ego is called the dream state[2] and the full manifestation[3] of the ego is the state of waking.
[1] Disappears- The ego merges itself in the causal ignorance which is characterised by the non-apprehension of empirical objects. This state in which there is no perception of duality is called the state of deep sleep. The ego in this state does not identify itself with the body. The result of past Karma, then, is not noticed. Therefore we become unconscious of our body in that state. Compare: “(Therefore he who has crossed that bank) if blind, ceases to be blind; if wounded, ceases to be wounded: if afflicted, ceases to be afflicted.”
[2] Dream state- In the dream state the ego does not perceive any object external to itself. The seer, the objects seen and the act of seeing which constitute the dream experiences are only the mental modifications of the ego. Compare: “There are no (real) chariots in that state, no horses, no roads (but he himself creates chariots, horses and roads).” The dream experiences, though they appear during the dream state as outside the body of the seer, are known to be only modifications of the mind from the standpoint of the waking state. Therefore from the waking standpoint the dream state is only a partial manifestation of the ego.
[3] Full manifestation- In the waking state the ego experiences the gross external objects by means of its internal organs. The ego and the non-ego which constitute the entire world of experience are both cognized in the waking state. In dream it is the mind alone of the sleeper which appears both as the ego and the non-ego. Therefore the full manifestation of the experience covering both ego and non-ego is seen only in the waking condition.” dRRig-dRRishya-viveka – An Inquiry into the Nature of the ‘Seer’ and the ‘Seen’ 1931, with English translation and notes by Swami Nikhilananda, Sri Ramakrishna Ashrama, 1976. ISBN 090247927X.