I made it very clear to my pt, drs, etc. that I would attempt to walk fine and then literally hit a “wall” out of the blue! My PT understood and took that into account when discussing my workout (which, by the way never went past a 1/2 hour!) I have seen a dramatic increase in time span before the “wall” sets in but it is still there just the same. Take heed to the idea of ensuring enough rest.