It has all the hallmarks of being a disease that is easy for a doctor to fuck up:

1. Affects different people in very different ways.
2. No objective biomarker.
3. Diagnosed by exclusion.

It’s always easy to miss things! I have a heart defect that was missed for years because it was constantly fobbed off as anxiety. It wasn’t until I started seeing a nurse for something unrelated did someone genuinely start to question what was going on.

Turns out my heart isn’t overzealous because I’m anxious, it’s because it’s making up for that fact it’s got some issues it’s trying to constantly correct on its own.

I got diagnosed with something with variable symptoms too, and most of the common ones overlap with yours, so yeah it could be other stuff