It sounds like you have - correct me if I am wrong - a sensorineural (nerve, inner ear) hearing loss in your left ear, with no middle ear problem (no fluid or blood) and no outer ear problem (no wax, debris or swimmer's ear).
There are many causes of sudden hearing loss like this, lots of them are related to systemic diseases (stroke, Lyme disease, Meniere's disease, etc...) but I would think that there are four main diagnoses that are being considered in your case:
1) Sudden Sensorineural Hearing Loss (SSNHL) - no one knows exactly what causes this, it is though to be an autoimmune response to a virus or some other agent, and the classic treatment is steroids. You should know that a recent large study found no overall definitive benefit to steroids, but this is a hard thing to study scientifically, and I think that if I had it I would also take steroids - not much of a down side and possibly some chance of improvement. If you want to read more,
here's something...
2) Barotrauma induced inner ear injury (perilymph fistula) - a leak of fluids from the inner ear, usually associated with rapid pressure change, and symptoms of dizziness. This is the one that you operate on with no way of proving it ahead of time. Can't see it on a scan, can hardly see it at surgery, but sometimes you can see fluid welling up around the oval window and you put some fat in there. If you have just seen a regular ENT doc and not an ear specialist (an otologist) you might want that consultation - PM me if you want me to see if I can give you a local referral.
3) Inner ear DCS - bubbles in the inner ear fluid. Again, usually associated with dizziness. Treatment is recompression, I will leave it to DDM and the other experts to comment on this, but my understanding is that a week is sort of late for a chamber ride. Interestingly, SSNHL is sometimes treated with hyperbaric oxygen, but this is not really standard therapy, and the data is mixed. So if you get a chamber ride for inner ear DCS and your hearing improves, that doesn't necessarily mean that it was DCS and that your doc could be right about the coincidental SSNHL.
4) Acoustic neuroma - a benign tumor of the nerve of hearing. That is the reason to get an MRI. 1, 2 and 3 won't show up on an imaging study.
SO, given that this happened after diving, and after fairly aggressive diving, I would say that it would be quite a coincidence for you to just randomly develop SSNHL at that exact time, or for an acoustic neuroma to suddenly cause the acute onset of hearing loss. Remember, I can't diagnose ANYTHING over the internet, but I'm just making some observations about what sounds likely and what is not likely.
Good luck, keep us posted!