Initially when I as mild I had only physical PEM. However, my coworkers at the time noticed the cognitive problems before I did. Embarrassing, but when your thinker is broken it's harder to notice that you can't think, I guess. Now I have both physical and cognitive PEM. Physical PEM is brought on by doing physical things- showering, standing. Cognitive PEM is brought on by physical or mental exertion such as reading.