i have a theory! i reckon that the more we have on our minds in waking life - the heavier our 'baggage', the weaker our perception of reality and awareness of the dream world becomes - its like we need to get away from reality, and dream stupid things and believe them just so we can feel more 'sane' when we wake up or something!

maybe dreams are like our brains acting as filing cabinets for all our subconsious thoughts - and if we have to many, it goes on overload and we are forced to just sleep and watch what happens and have no control over it!