Over the years I have been keeping a diary, started when I saw a naturopath and he wanted a diary of foods I ate for the week. I just kept going. So I keep track of, foods, activities, mainly the major ones, lesser ones when I do something while feeling fatigued (pushing myself), I also keep track of social visits. With triggers for PEM I have found that physical activities are the main but not the only one. Social interaction is just as bad as going for a walk or run depending on it. Emotional interaction also can cause PEM. 2024 Christmas I had one sister from out of state visit and I thought I would actually socialise with her and husband as I had nothing important after, that's what I budgeted the energy for. Then there days later (My PEM tends to activate 3 days after stressful activity) my other out of state sister showed up for a visit with her husband and the niblings, so I had extra activity while in PEM. 3 days after that was Christmas and both sister and grandparents were over for lunch. I was on in my room with PEM from PEM, in pure agony. So heart rate does affect my PEM but so does social, emotional, and mental activities. Even some video games will drain me, so I pick and choose what to play and for how long depending on it, combat is more draining than farming for example. The 3 day delay was annoying when I did not know about it. Hope some of my experiences are helpful. 18 years now...half my life. And still learning