If I were you, I wouldn't worry about it too much.  If an occasional bout of performance anxiety is the worst of your troubles, you're doing all right.

Besides, if you are on-time, clean, and polite, most any provider would consider you a great client - ED or not.

The problem with performance anxiety is that it is a feedback type thing - you worry about it, so it starts to happen, so you worry even more, etc.  Accept that it might happen, but don't let it ruin your time.  Just figure that you'll find other things to do.    Good thing that most of these ladies are professionals.  They are trained for just such an emergency!