dreaming - A dream is the experience of envisioned images, sounds, or other sensations during sleep. 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 a dreamer realizes that he or she is dreaming—being sometimes even capable of changing the oneiric reality around him or her and controlling various aspects of the dream, in which the suspension of disbelief is broken.[citation needed] Dreamers may experience strong emotions while dreaming. Frightening or upsetting dreams are referred to as nightmares. The scientific discipline of dream research is oneirology.