I just came back from an EMG session with my neurologist. After the tests, which showed that most of my nerve conductivity in my (weak) left leg is at the borderline of normal, she reminded me that in my previous MRI's I had shown evidence of degenerative bone disease in my lower spine. This means that a good part of my foot-drop, mobility and left-leg weakness problems could be caused mostly by that, not my MS! If that is the case, I'm not sure what it means with respect to therapy and lifestyle, but perhaps it means I need to develop different coping techniques than what I was using. Now I have to wait for a new MRI to see... Of course, lower back problems don't explain my weak left arm, but who knows, maybe I have some upper spinal problems, too.
PS: It's great having a neurologist who is willing to look beyond my MS to see if some of my symptoms don't have other causes!