Okay, I have an update.

My blood has been tested for white/red count, platelets, kidney function, liver function, thyroid, and various other nutrients like b12 and potassium, and all of those are 100% fine. So It seems highly unlikely to be anything serious. (Am I right FMP?)

This is on top of knowing I haven't got Flu, Mono, or Strep. So a virus seems like the most likely candidate. Plus anxiety of course.

I now also have a referral to a neuro and an ENT, so hopefully those appointments go well, and I can finally put this horrible episode behind me.