Why do we dream when we sleep?

Question

I have often found myself wondering this, and then find myself very angry because i cannot figure out the answer. Why do we dream when we sleep?

Answer 1

I have heard that Dreaming is the Brains way of getting rid of excess information or input, that it has received through out a period of time, it does it at the most convenient time = when we are sleeping. That would answer the question of why a lot of dreams make absolutely no sense whatsoever.  

Answer 2

Don't be angry- psychologists haven't reached a consensus yet either.

Some will say that it is the brain trying to make sense of random firings of memories and thoughts during the night, psychodynamic theorists say that it is the unconcious acting out it's repressed desires and the ego covering them up so we don't get scared..

there are other explanations as well, there are just the two I can remember from the top of my head