Dreams are a normal physiological and psychological phenomenon that occurs during sleep. They are a special imaginary activity without conscious control.

Freud, based on his psychoanalytic theory, viewed dreams as unconscious processes, manifestations of suppressed wishes and conflicts. Pavlov's theory of advanced neural activity believes that sleep is a diffuse inhibitory process in the cerebral cortex, and dreams are excitatory activities that occur under this inhibitory condition under the influence of various stimuli inside and outside the body. Modern physiological research believes that sleep can be divided into two phases: fast wave sleep and slow wave sleep. At the beginning of sleep, you first enter slow wave sleep, turn into fast wave sleep 1 to 2 hours later, and turn into slow wave again about half an hour. During the entire sleep process, the two types of sleep are converted repeatedly about 4 to 5 times. Most dreams occur during rapid wave sleep. It is generally believed that dreams are basically the continuation of people's thoughts, emotions, needs and desires during awakening, and are related to what they think about during awakening.

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