Dreams occur during REM sleep and have both manifest and latent content. There are three main theories that attempt to explain dreams: Freud's wish-fulfillment theory which sees dreams as revealing unconscious desires; the information-processing theory which views dreams as sorting memories from the previous day; and physiological function theories like the activation-synthesis theory which suggests dreams give meaning to random neural activity during sleep. REM rebound refers to increased REM sleep after periods of REM deprivation. Lucid dreams involve realizing you are dreaming and controlling the dream. Common dream themes include daily events, sex, falling, and being attacked.