"Understanding waking consciousness, sleep and dreams depends on how the lines are drawn among them," writes author Siri Hustvedt. "Ernest Hartman at Tufts University School of Medicine proposes a waking-to-dreaming continuum, a range of states that move from highly self-conscious, logical, category bound, sequential wakefulness to daydreaming and reverie with their more fragmented, less logical thoughts to dreaming. ... We may not know why we sleep, dream or wake up, but these states are never static."