“Common sense tells us that we become unconscious the moment we fall asleep at night, and come back to full consciousness again in the morning. That idea was challenged when REM sleep was discovered some 5 decades ago. The EEG traces that signal waking consciousness are fast, irregular and low in voltage. Brain activity in REM sleep looks exactly like that…

People waking from the least conscious state (Slow-Wave Sleep) still report experiences of “mentation” — fragments of verbal thoughts. The most radical interpretation is that we are never fully unconscious, even when in deep sleep without dreams. This seems totally against common sense…

During the most unconscious state of sleep, the brain may be like a great city at night. Most of it may look dark, but there could be local spots of meaningful activity going on even then…” Science And Consciousness Review