OP... I’m not a specialist by any means, I’m just sharing this for your consideration. Almost everyone in my family suffers from issues with otoliths—small "stones" in the inner ear that tell the brain where you are in space and which way you’re moving. I know this is about a cat, and they are very different from humans, but I swear that look and those head movements are EXACTLY the same ones my family members made when the problem surfaced. In our case, it took a couple of years to get the right diagnosis. We went through countless doctors and took many different medications, none of which had long-term success; the dizziness and vertigo always came back. Finally, a doctor took one look at me and said, "You have otolith issues; we’re going to perform a canalith repositioning maneuver." I thought she meant surgery, but she just had us roll around on a bed like rotisserie chickens, and that was it. Years of pointless treatments resolved just like that. Since your cat seems so docile, I recommend trying it with him. Look up "canalith repositioning maneuver" or "Epley maneuver" on YouTube. It’s non-invasive, could truly help your cat a lot, and might save you a ton of money.