Series of thoughts, images, or emotions occurring during sleep, particularly sleep accompanied by rapid eye movement (REM sleep). Dream reports range from the very ordinary and realistic to the fantastic and surreal. Humans have always attached great importance to dreams, which have been variously viewed as windows to the sacred, the past and the future, or the world of the dead. Dreams have provided creative solutions to intellectual and emotional problems and have offered ideas for artistic pursuits. A type of cognitive synthesis that facilitates conscious insight may occur subconsciously during dreaming. The most famous theory of the significance of dreams is the psychoanalytic model of Sigmund Freud; in Freud's view, desires that are ordinarily repressed (hidden from consciousness) because they represent forbidden impulses are given expression in dreams, though often in disguised (i.e., symbolic) form.