OK, this is my understanding.
When you sleep, your heart rate slows down. When you wake up (and become active) your heart rate speeds up and your body gets a rush of blood. And what causes hard-ons? Blood flow. So, that's why you get morning wood.
I guess it could be right, but by that same logic, you would get wood during a football game or a race (some of us do, lol).
I don't know. All that I know is that it makes damn hard to take a piss in the morning. You have 3 options. The first is to try to hold it in till the wood goes away. The 2nd is to try to brace yourself on the wall and hope that you can point that fvcker downwards. The 3rd I have never tried *cough* but I guess you could just hop in the shower and pee on the wall.
-Ducky