I had Lyme for many years before I developed ME, so I was used to being exhausted and getting ill if I did too much.
However with ME the strange thing, which was new to me and I suspect unique to ME, was that intellectual activity could make me physically exhausted, weak and in pain. Emotional activity or stress could make me intellectually incapacitated, unable to make even the simplest of decisions.
It seems that ANY activity or effort, no matter what kind, affects the whole person including physically, mentally and emotionally.
This is very challenging to manage, trying to keep ALL types of activity to a very low level in order to be able to function when it is necessary.