The brain is like a hard disk and the mind is like an operating system. When we sleep, it wanders along on screensaver. It picks out data at random and reacting to our surroundings and our physical conditions, creates scenes out of our subconscious thought patterns and strings them together into a story. That explains why we sometimes can even continue on a dream when we go back to sleep after getting up in the night.
Sometimes they resemble our past because it picks on images out of our vast store of memories. Sometimes they piece together random images of people and places and they blend them together to become faces or places we’ve never seen or been before or an occasion we've never experienced at all or an event that's yet to happen or never happened at all. Ever remember once in a while you're doing something or at some place and you thought you'd been there or done that? Ever met someone you thought you'd met before? Probably it's true, but it's only in your dreams.
That’s what a dream is all about. I think.
Thanks to Bengbeng for triggering this thought process.