Book excerpt: Fragmented, dissociated consciousness can characterize the mind in both wake and sleep states. Dissociative symptoms, during sleep, include vivid dreaming, nightmares, and alterations in objective sleep parameters (e.g., lengthening of REM sleep). During waking hours, dissociative symptoms exhibit disparate characteristics encompassing memory problems, excessive daydreaming, absentmindedness, and impairments and discontinuities in perceptions of the self, identity, and the environment. Llewellyn has theorized that a progressive and enduring de-differentiation of wake and dream states of consciousness eventually results in schizophrenia; a lesser degree of de-differentiation may have implications for dissociative symptoms. Against a background of de-differentiation between the dream and wake states, the papers in this volume link consciousness, memory, and mental illness with a special interest for dissociative symptoms.