People do not realize that the PT's actually work for you. It is difficult to say "no" when you are a bit drugged up, but you may want to discuss this in the future and set up some parameters as to what you will do and what is acceptable---and what is not.
I agree---it was waaaaay too early for the Nu-Step, and you should never hurt or be in pain or during PT---take everything to the point of discomfort only.
As others will tell you, it is not about the "no pain, no gain" approach---but it is, rather, "no pain, more gain" that will help you out---it seems like the PT instituted a "surprise attack" on you. Let them know that you will not allow this activity again.