I have this theory (kinda borrowed from a Richard Linklater movie) that when people are about to die, that 1 second in which their brains are about to shut down, time slows down, and during that second we experience our wholes lifes again, in our minds. And when we get to that last second, time slows down again, and we experience life again on that first experience, and so on (if you know the famous Zenon paradox about the arrow and the soldier, you get the idea). BUT, when we experience our lifes again, our subconscious mind changes a few things. That girl who ignored us at highschool, now she merely smiles, on the next one she talks to us...

And our dreams are som sort of "post it" notes on our minds, reminding us of things that are about to happen or already happened in our lifes...