heathfield, you make a good point there I think. A nightmare will wake you up. I get very few of them, fortunately, but at one time I used to dream quite often about falling from a great height, and I�d always wake up before I hit the ground!
Another thing which puzzles me is ... why is it that you can sometimes awake during a dream (which seemed very real at the time), but remember nothing about it? I think it�s because the brain sort of goes off at a tangent and there�s no logical thread to it which you can interpret in a waking state.