Consciousness is a state of awareness. Daydreams are a period of thinking and feeling not bound by logic. Divided consciousness refers to the splitting off of two conscious activities that occur simultaneously. The unconscious mind processes information without our being consciously aware.

Sleep begins as we enter a semiwakeful hypnagogic state and becomes progressively deeper as we enter dream sleep. We typically enter REM sleep four to six times each night. REM sleep, accompanied by dreams, rapid eye movement, and by an "autonomic storm," is not the only part of the dream cycle that is filled with dreams. The nature of non-REM dreams differs from REM dreams. Sleep cycles follow a pattern called the circadian rhythm. Most of the conscious experience in dreams is visual, and most dreams have some positive or negative emotional content. Much of the content of our dreams is directly related to things going on in our waking lives, a term called day residue. Freud distinguished between the manifest content of dreams and the latent, or symbolic meaning of dreams. Sleeping and dreaming seem essential to physical and physiological health; sleep deprivation brings on fatigue, inefficiency, and irritability. Nightmares, night terrors, sleepwalking, and sleeptalking are fairly common sleep phenomena.

Three types of sleep disorders are insomnia, narcolepsy, and sleep apnea. Altered states of consciousness share several common characteristics, including distortions of perception, intense positive emotions, a sense of unity, and others. Many persons achieve a very relaxed state by a process called meditation. Hypnosis is sometimes used to alter consciousness and to relieve pain. Depersonalization is the experience of one's body or surroundings becoming distorted or "unreal" in some way.

Consciousness can be altered through the use of various psychotropic drugs. These may be classified as stimulants, depressants, inhalants, and hallucinogens. Although risks differ from drug to drug, all drug users run the risk of abuse, dependence, addiction, and direct or indirect side effects.

Stimulants are drugs that activate the central nervous system. Even mild stimulants like caffeine and nicotine are physiologically addictive. Amphetamines and cocaine are other highly addictive stimulants. Depressants influence conscious activity by depressing parts of the central nervous system. Alcohol, tranquilizers, sedatives, and narcotics are all depressant drugs. Inhalants are usually toxic and often cause brain damage. Hallucinogens alter perceptions, cause hallucinations, and are often associated with bizarre or violent behavior. Psychological dependence is common with hallucinogens. Marijuana is a popular although illegal drug that produces a sense of well-being and sometimes alters perception. Health risks are also associated with the use of legal consciousness-altering drugs, such as caffeine, nicotine, and alcohol.