Before turning to the Indian debate, I would like to motivate the examination of dreamless sleep and consciousness by considering the experience of waking up from deep sleep and what this experience reveals about our experience of the self.
One of the best descriptions of waking up comes from Marcel Proust. In a long passage at the beginning of the first volume of In Search of Lost Time, the unnamed narrator describes awakening from sleep:
A sleeping man holds in a circle around him the sequence of the hours, the order of the years and world. He consults them instinctively as he wakes and reads in them in a second the point on the earth he occupies, the time that has elapsed up to his waking; but their ranks can be mixed up, broken. If towards morning, after a bout of insomnia, sleep overcomes him as he is reading, in a position too different from the one in which he usually sleeps, his raised arm alone is enough to stop the sun and make it retreat, and, in the first minute of his waking, he will no longer know what time it is, he will think he has only just gone to bed. If he dozes off in a position still more displaced and divergent, for instance after dinner sitting in an armchair, then the confusion among the disordered worlds will be complete, the magic armchair will send him travelling at top speed through time and space, and, at the moment of opening his eyelids, he will believe he went to bed several months earlier in another country. But it was enough if, in my own bed, my sleep was deep and allowed my mind to relax entirely; then it would let go of the map of the place where I had fallen asleep and, when I woke in the middle of the night, since I did not know where I was, I did not even understand in the first moment who I was; all I had, in its original simplicity, was the sense of existence as it may quiver in the depths of an animal; I was more bereft than a caveman; but then the memory—not yet of the place where I was, but of several of those where I had lived and where I might have been—would come to me like help from on high to pull me out of the void from which I could not have got out on my own; I passed over centuries of civilization in one second, and the image confusedly glimpsed of oil lamps, then of wing-collar shirts, gradually recomposed my self’s original features. (Proust 2003, p. 9)
Proust depicts the moment of awakening from deep sleep as one where we have lost all sense of the self derived from memories of the episodes of our lives. Instead of the autobiographical or narrative sense of self as a person with a storyline through time, there remains only the sensation of existing at that moment. What marks the first instant of awakening is not the self of memory but the feeling of being alive, or what Proust calls “the sense of existence as it may quiver in the depths of an animal.”
The moment of awakening thus reveals two kinds of self-experience. The first kind is the embodied self-experience of being alive in the present moment, or the experience of being sentient. The second kind of self-experience is the autobiographical experience of being a person with a storyline, a thinking being who mentally travels in time. The first kind of embodied sense of self we experience immediately upon awakening, but as we reach automatically for the second kind of autobiographical sense of self, it sometimes goes missing.
This distinction between two modes of self-experience, one of which remains present in the sleep–wake transition even if the other is lost, suggests the following tentative phenomenological line of thought leading towards the idea of consciousness being present in certain phases of dreamless sleep.
Consider that although deep sleep creates a gap or a rupture in our consciousness, we often feel the gap immediately upon awakening. Our waking sense that we were just asleep and unknowing is not outside knowledge—like the kind we have when we know about someone else’s having been asleep; it is inside, first-hand experience. We are aware of the gap in our consciousness from within our consciousness. Although we may forget many things about ourselves when we first wake up—where we are, how we got there, maybe even our name—we do not have to turn around to see who it was who was just asleep and unknowing, if by “who” we mean the sense of self as the embodied subject of present-moment experience in contrast to the sense of self as the mentally represented object of autobiographical memory. This intimate and immediate bodily self-awareness that we have as we emerge from sleep into waking life suggests that there may be some kind of deep-sleep awareness, operative at least for some stretch of time prior to waking up, a taste of which we retain in the waking state, despite there being no specific mental content to recall. If there is a deep-sleep awareness we can retain in this way, then there may, at least for certain phases of deep sleep, be a phenomenal character to deep sleep or something “it is like” (Nagel 1974) to be deeply asleep—in which case consciousness cannot be entirely absent from deep sleep (Sharma 2001).
This line of thought finds its strongest philosophical expression in classical Indian philosophy, so if we wish to see whether we can sharpen it into a more compelling argument, we need to look at the Indian discussions.