For experiments showing consciousness during non-REM sleep using serial awakenings, see Early-night serial awakenings as a new paradigm for studies on NREM dreaming and Assessing sleep consciousness within subjects using a serial awakening paradigm.
For the discussion of dreamless sleep in Indian philosophy, see Evan Thompson’s paper Dreamless Sleep, the Embodied Mind, and Consciousness.
For the argument that white dreams might not just be an instance of forgetting but might be reflective of the experience itself, see Jennifer Windt’s paper Just in Time—Dreamless Sleep Experience as Pure Subjective Temporality.
For the commentary about experiments on odor-induced memory consolidation during deep sleep, see the Walker paper Memory Processing: Ripples in the Resting Brain.
For the review paper summarizing these findings by Windt and Thompson, see Does Consciousness Disappear in Dreamless Sleep?.