Oliver Sacks' A Leg To Stand On is a lengthy discussion of that, including his own experiences after breaking a leg---IIRC, at one point after surgery but before he starts physical therapy, he wakes up convinced that a medical student has played a prank by removing his leg and attaching one from a cadaver, or at least sticking a cadaver's leg under his blanket. (ISTR he tries to throw it out of bed and ends up on the floor.)