Sri Aurobindo reminds us that the use of the terminology of “dream-state” and “sleep-state” for the stages of the trance of Samadhi is symbolic in nature, so that we can try to relate it to some experience we have in our normal human consciousness; however, it is important to remember that this is symbolic language only and not a precise description of the experience. Just as the “dream-state” accesses the inner vital and mental planes, the “sleep-state” accesses higher planes of awareness that are not normally accessible to the mental waking consciousness. Thus, when entering into these higher states, the transcription of the mind is of deep, dreamless sleep. Sri Aurobindo clarifies however that this is not really a “sleep” experience: “It is not the truth that the Self in the third status called perfect sleep, susupti, is in a state of slumber. The sleep self is on the contrary described as Prajna, the Master of Wisdom and Knowledge, Self of the Gnosis, and as Ishwara, the Lord of being. To the physical mind a sleep, it is to our wider and subtler consciousness a greater waking.”
When the consciousness exceeds the boundaries within which the physical consciousness can perceive and respond to it, there is appearance of a blank or emptiness that seems to be sleep. Through training, the mind can extend the reach of the normal waking awareness to a certain extent. “This border-line varies with the power of the individual consciousness, with the degree and height of its enlightenment and awakening. The line may be pushed up higher and higher until it may pass even beyond the mind. Normally indeed the human mind cannot be awake even with the inner waking of trance, on the supramental levels; but this disability can be overcome. Awake on these levels the soul becomes master of the ranges of gnostic thought, gnostic will, gnostic delight, and if it can do this in Samadhi, it may carry its memory of experience and its power of experience over into the waking state. Even on the yet higher level open to us, that of the Ananda, the awakened soul may become similarly possessed of the Bliss-Self both in its concentration and in its cosmic comprehension. But still there may be ranges above from which it can bring back no memory except that which says, “somehow, indescribably, I was in bliss,” the bliss of an unconditioned existence beyond al potentiality of expression by thought or description by image or feature.”
These ranges beyond the ability of the waking consciousness to partake in any direct way are what can be called the “sleep-state” of Samadhi.
Sri Aurobindo, The Synthesis of Yoga, Part Two: The Yoga of Integral Knowledge, Chapter 26, Samadhi, pp. 504-505