Unfortunately, being anxious is about Enemy #1. Ask me how I know. No, really...go ahead.
You are posting this early at zero-dark-thirty according to my clock, but maybe you're a lot further east. That would account for some of the time. Still, you're outta ammo and you have come here hoping for magic. That particular ingredient is in the rarest form of supply here.
I have been in your shoes, honestly. It took a few trials with me telling myself it really is the stomach distension that is setting off my AF. As far as I know, I got that right...eventually...and was careful until my first ablation and beyond. As my sergeant instructor told me all those many years ago at officer candidate school, any fool can be uncomfortable. Another lesson for me. It takes foresight, learning, and self-discipline.
Dehydration, over-exertion, disease, infection, inflammation, mineral imbalance,...there are several things that can cause an elevated or wonky heart-rate. I don't see how a log-grade fever would be a normal response to stomach distension, or to too much of the wrong food, unless one is sensitive to MSG, for example, or has a Vagus response to GERD (which might be at play here). Even then, why a fever and not just SVT, PACs, or AF?