I'm not going to get into the moral issues about cheating on your wife. As they say, that is out of the scope of my practice. That will have to be between you and your own conscience, you and your "higher power" or you and a therapist, which sounds like the best bet since you are so freaked out by this. They will be able to put this "mistake" into perspective for you and help you learn how to forgive yourself and move on.
Did you use condoms when you were with the pro? That should alleviate many of your fears right there. And you spoke with a doctor on the HIV forum who reassured you that your chances of having contracted an STD or HIV are slim to none. It's your guilty conscience that keeps you awake and not eating and so horribly afraid.
Getting to your questions........yes, you should have yourself tested as soon as possible, even if for no other reason than what the forum doc said.....to relieve your own mind. I don't think I'd leave this up to a prostitute. You said you paid her to get tested. And how, exactly, will you be sure she actually did? I think you need to be "man' enough to see this through despite all your fears, which you brought on yourself. Time to take some responsibility and do the right thing. If not for you, then for your "wonderful and loyal" wife.
When will you begin to feel better and how will you deal with the shame of cheating on your wife.............those, my friend, are questions you will be dealing with for a very, very long time.
Get tested.
Get into therapy.
Keep it in your pants.
Greenlydia