When I started working with a fitness trainer to help me alleviate/manage chronic knee pain after endless visits to the doctors, physio, pain meds, and being told my knees were weak, the first thing he told me after I described my issue was "this is all in your head, your knees are OK.". Of course that's not in the same context you're describing here, but it boils down to the same thing I guess. I reckon I remained with the memory of pain or I manufactured it long after it had gone...or not. Interestingly, true to his word, when I started working out with the same pain and weak knees, and he kept repeatedly telling me the pain was in my head, the pain went away...fascinating!!!