Dreams are generated by the brain. Although they sometimes incorporate images of real people or places in life, or even reflect actual events from a dreamer's waking existence, they are not actual events.
Scientists are unsure why people dream. Some scientists believe it is the way in which the brain processes and makes sense of the information it receives. Others believe that it is simply a way for the brain to determine what is necessary to retain and what is not. Still, others believe that dreams are nothing more than the random flashing of images as people sleep.
Regardless of their divergent theories about why people dream, however, scientists agree on many of the primary physiological aspects of sleep. Partial paralysis is one of those. When people enter R.E.M, the deepest form of sleep, the body partially paralyzes itself in order to prevent an individual from being able to act out his dreams.
Also, some people are lucid dreamers. Lucid dreamers are those individuals who are aware that they are dreaming and are able to remember many aspects of their dreams in detail even long after they have awoken and risen. In contrast, most people forget their dreams shortly after waking.