Totally agree. It's exertion of any kind that can cause PEM for me, not just exercise. I haven't exercised in over a year, but I've had lots of PEM crashes. And my "energy envelope" also seems much smaller than it used to be. With each big PEM crash I have not recovered to where I was pre-crash no matter how many months of rest and avoiding PEM I managed to pull off afterwards. And none of the crashes were from any major exertion either, just too much for my system.