Update - after 14 days of prednisol, my hearing's back to what it was. Luckily it started returning piecemeal in the first seven days, before I even had a chance to see an ENT. I've seen two ENTs since (including the one recommended by DAN) and they both said there should be no correlation between my freediving and the ISSHL.
I still have tinnitus in my left ear and don't know if that will ever go away. The ENT says it could go away in a day, a week, or stay forever. It's annoying but I am able to tune it out most of the time and I'm just happy my hearing is back. Being deaf in one ear felt like I had a giant ball of ear wax in front of my eardrum, or was wearing an earplug. I constantly wanted to shake my head and get the blockage out but of course the outer and middle ear were empty. I did one hyperbaric chamber session but at $400 a pop out of pocket, I decided one was enough as my hearing had returned.
Ukmc: Both ENTs did an audiogram, inspected my outer ear, and inserted some kind of thingie in my outer ear to test the middle ear pressure. I'm not sure how they checked for barotrauma but to me, there's no reason for it to be barotrauma as I could and still can equalize fine and had no balance issues or pain/nausea. I've been (free)diving for 30+ years and have never had any issues clearing and am well aware of what to look for when descending/ascending.