Dream
Dream is the friends of sleep . some people sleeping will dreaming . When you sleep , our subconscious mind will come out and go around ,has some fun. So that's why we seldom dreaming. I think everyone do dream in night while sleeping . Some dreams are very good but some are vary funny but many of them are very dreadful . If we dreaming while asleep is show that its not a good night sleep. When you wake up you will feel more tired . 

Based on research human beings dream , and so do , scientists believe, most mammals and some birds. On the most basic level, a dream is the experience you have of envisioned images, sounds or other sensation while you sleep. They are an internal mental process.But dreams are actually much more than that. 
What are nightmare?
Nightmare are vividly realistic, disturbing dreams. There can be a number of psychological triggers that cause nightmares. For example, anxiety and depression can cause nightmares.