Is this PEM, or something else?

So I don’t get this often, but It’s some thing that I’ve tried very hard to avoid ever since experiencing it.

Sometimes when walking around, exerting myself , it’ll feel like my heart is getting tired. My chest starts aching. My heart starts working harder, it gets stuck on that sensation that you feel in your chest when you need to take a deep breath and you’re not getting enough air.

While I’m moving around, it typically won’t leave this phase . But when I stop and start resting, if I’ve done too much, my heart starts beating a lot weaker. Sometimes it’ll then progress to squeezing pains in my chest, plus blood pressure dysregulation, tinnitus, and other autonomic symptoms. In the worst of times, suddenly it feels like my heart stops “ trying”, and quickly switches to a mode where it’s beating very softly. When it does this., it feels like a blood pressure change spreads out from my heart to every vein in my body. My muscles feel incredibly weak, and in that moment, I’m more tired physically than I’ve ever felt in my life.

Generally, I have more dysautonomia symptoms in the days following these events. These can last a very long period of time, and they progressed to the point at one time where I had pretty significant POTS type symptoms.

For the longest time, I thought that this was a heart specific thing , and was visiting cardiologist to try to get it figured out. Then I realized it was Covid and thought it was a form of dysautonomia. But the more I read about PEM the more I wonder if this is what it is. Has anyone experienced anything like this?