h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

How come whenever you have one of thoes dreams that is a real humdinger,you know the kind-intense,extremely vivid ,go on for hours weird as hell,twenty seconds after waking you cant remember a thing?
Sometimes you think you can remember until you start to relay it,then whoosh its gone, your dream suddenly turns to "no,or was it a horse" "it'll come back in a minute",ha,what a con.

Basically, the mind has several states. I have occasionally been drifting off to sleep only to remember whatever I was dreaming about the previous night!

Billy Connoly once said that he has two memories: A drunk one and a sober one. It's similar to that, I guess!