another metaphor i like is buying a high mileage car. everything is at the end of its life - the motor, the tranny, the rear differential. most people choose to replace the motor first because they can feel and hear that right off. the new motor gets in and the pedal goes down when you drive - vroom, vrooom. pop goes the tranny because it could handle being babied along withthe old motor being weak, but put renewed power to it and the weakest link in that snaps. replace the tranny and a new rear end isnt far behind.
the body rebuilds from the inside out. gotta give it time and not break something in the meantime just because one part is humming along better than ever. when it comes to living whings, use it or lose it. start slow and build up strength. thats how it works.