Is it possible to work your limitations into the RP?

Have you considered a walker for these events? Maybe dress it up as a horse or the lower half of one an become a centaur? I also used to LARP and still do a fair bit of RP, there's fit to be a way to work in an aid that will help you enjoy your time without getting overextended. I use a walker for some of my bigger family events so I can do better at keeping up or just sit down when I need a break even if there are no traditional seats.