Dreams.
A dream is the experience of envisioned images, sounds, or other sensations during sleep. It occurs in humans, most mammals, and some birds. The events of dreams are often impossible or unlikely to occur in physical reality, and are usually outside the control of the dreamer. The exception is lucid dreaming, in which dreamers realize that they are dreaming, and are sometimes capable of changing their oneiric reality and controlling various aspects of the dream, in which the suspension of disbelief is often broken. Dreamers may experience strong emotions while dreaming. Frightening or upsetting dreams are referred to as nightmares.