This document discusses different levels and states of consciousness. It defines consciousness as a mental state of awareness of one's self and environment. It describes Freud's model of consciousness, including the conscious, preconscious, and unconscious levels. The unconscious level contains unacceptable thoughts and desires that influence behavior outside of awareness. The document also discusses altered states of consciousness like sleep, drugs, and hypnosis. It explains REM and NREM sleep cycles and the four stages of NREM sleep.