"Are there times in a day that you just feel horny or wet in anticipation of sex?"
Yes, all adult human beings get horny unless they are asexual. The human mind/imagination is a beautiful thing.
"Have you ever had an orgasm in your sleep?"
Personally I have not, and I never understood how people do...don't you have to be, like, stimulating yourself in order to have one? How could you masturbate in your sleep (I guess it's like sleep-walking...only with an orgasm...but then wouldn't you wake up?)? Maybe you could answer that one for me, hehe..
"Aside from being a guy, I have no idea why I wake up with a hard-on but it never ceases to amuse me :)"
It is quite amusing to me too. I know it has to do with increased blood flow to the d*** during R.E.M. The mysteries of sleep...
As a side note, the ancient Chinese considered waking up with a hard-on to be a sign of fertility. Certainly it is one aspect of male fertility :)