I findd it is because you have to piss. I always have to piss if I wake up with an erection. I believe it stops you from urinating in your sleep, however, I'm not sure.(it's harder to piss if you have a hard on, so that's why none seeps through as apposed to when you are flacid)..
It's normal. It can suck if your mom comes in to get you and you've got this major hard on rofl..
All my friends are skeletons,
dulcimers and chariots
prayers to God, oh prayers to God
Was I sleeping all this time?
Was my shadow ever mine?Wintersleep-Danse Macabre