Previously, there were several theories regarding this issue. According to Sigmund Freud's version, dreams are suppressed and unfulfilled desires and dreams of the dreamer, they appear as a result of the systematization of information, or are preparation for difficulties. This allows the brain to solve complex problems in a dream, preparing the mind for solving problem situations in reality.
Professor Deirdre Barrett believes that sleep acts to some extent to mobilize resources for solving certain problems that the brain explores in sleep. This assumption is confirmed, for example, by nightmares that torment people after difficult stressful situations experienced in life.
There is another version that sleep is a protective evolutionary mechanism, since the brain continues to remain active during sleep. Experts believe that in the brain in a dream, neurons can make up for losses, from which the brain reproduces in dreams all the experiences that happened during the day. If the recovery process was not completed in a dream, then by morning the person will not remember what he dreamed about.