I become exhausted after phys exertion, too; however, my main concern in flying is Neuro fatigue. I can become overwhelmed by too much input. I went to a grocery store during a flare and the sights, the variety, the sounds— all too much. ( which is just bizarre! And was upsetting). I echo the comment above: it IS SO weird! We can have same symptoms but they are triggered by different things and they manifest differently. It’s crazy-making. I have to fly in a few weeks and have my fingers crossed. Good luck.