Excerpt from “Dreamless Sleep, the Embodied Mind, and Consciousness" by Evan Thompson:
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.