I have mild vertigo and a chiropractor said the top of my spine was ever so slightly out and this can mess with nerves and balance. He fixed it for me and i definitely have noticed a difference. maybe something to look into?
This may be something that's completely obvious and that you've already tried, but those are the EXACT symptoms I was having before I got prescription glasses. On and off, though not super often, I would get these really rough bouts of vertigo that would last anywhere from 3 hours to a full day. After noticing that it'd usually happen after I was intensely focusing on something (like a computer screen, paperwork, small print, etc), I started to ask some questions and found out that my dad had had the same issues. His problem was resolved with glasses, so I followed suit, and sure enough, haven't had a single issue since getting prescription lenses. I'm sorry you've had to put up with so much to get an answer! Hope you soon find a resolution.
I get it too especially after a cold or if I get water in my ears.
I get it too especially after a cold or if I get water trapped in myveard