Hey Willy,
It makes perfect sense, it's a fine balance and it takes a lot of trial & error to figure out the right limits for your body. I know I get all energized & determined & then I go gung ho for exercise (bike riding, walking or some low impact good for you exercise) and I'm dragging & dying the following days. So it's really hard to figure my limits but I try. And most times it works out ok, when it doesn't I just wait for my body to catch up.
The way I understand it, the message doesn't get to the muscles from the nerves so the muscles can't "talk back" to the brain to tell us when it's too much. It seems to be about communication with this disease. :)