Sorry to hear that.
I've had it and it didn't hurt. I sort of felt an odd mild popping/cracking sensation but nothing painful. I describe it as like the sensation you get when eating popping candy, weird but not hurting. It was more of a sensation/sound than a real feeling, certainly not painful and lasted only a split second.
Were you particularly worried or stressed leading up to it that could have caused you to faint? Could you use relaxation/deep breathing techniques to help you tomorrow? You might find it less of a surprise and be able to handle it better.
Its so worth having it doen to save your sight