Why are you thinking it's the Nortriptyline? Don't you think the improvement must be related to adding the Gabapentin? What is the current dose of each now?

To answer your question: I think we probably all have stopped or backed off the dose of medicine we take when feel thing s are working...just to test to see if the pain is as bad as it was. It usually is. But it's normal to test this just to see if the nerves have 'healed' or if it's just the medication helping.

I don't think you are "damaging" your nerves in any way. Your actions probably just stir up the nerves and you see how sensitive they are to stimuli.