You need to go to the ER. It is not going to be pleasant, but you can have serious problems if you do not get this taken care of. Once they check you in, basically what will happen is a doctor will make a small incision in the skin of the penis and drain the blood so that the erection goes down. I know it sounds awful, but your other alternative is waiting until your bladder basically bursts because you can't pee when you're "up."