Dreams - why, which, where

I can put my hand on my heart and say that just about every night I will have a dream that alternates between snakes and flying. I have gotten so used to these dreams that when I used to get bitten by the snake and wake up I now sleep through it. The same is said for falling, flying and all that, I used to wake up with gasp, now I hit the ground and move to the next dream.
I have the definite ability to remember a lot of my dreams although I have heard you begin a new dream every few minutes. By the way, according to a popular dream book, snakes are supposed to be interpreted that someone you trust will stab you in the back. Snakes however would by far be my favourite pet or animal, but I suppose you never know...
There are two theories on why we dream, the physiological and the psychological. The psychological is to me, the most interesting and Aristotle wrote about the connection between dreams, experiences and needs. Some believe dreams to prophetic as written in the Bible and others believe, as Freud did, any number of things buried deep in our memory.