For what it's worth, my physiotherapist said that his experience, from the patients he's dealt with, is that the increased symptoms that follow a setback are typically temporary, and that after a short period of time (often 2-3 weeks) the patient usually reverts back to their prior state.

I had a significant setback myself. At 9 months post injury, I slammed a cupboard door against the side of my head, quite hard... (there were some pots/pans that were about to fall out of the cupboard, and my instinct was to slam the cupboard door shut, not being mindful of the fact that my head was in the way!).

My symptoms spiked, and I feel like it may have cost me 4-6 weeks of recovery time. But after 4-6 weeks, I do think that I reverted back to my prior state.