Here is my wife's answer:
Having been diagnosed with Meniere’s Disease about 12 years ago, I can share my individual thoughts as from personal experience and research only, not as a medical authority. First of all, I am sorry to hear of your situation. I hope that you are in the care of an ENT with specialization and breadth of experience in treating Meniere’s. Not all ENT’s delve in to this area in depth. The guidance of your ENT is of greatest validity. Perhaps there is one who also has diving expertise. I saw a few before finding the one who has managed my situation long term. I was referred to him by several others with Meniere’s in my area (found via a local support group). Your ENT office may be able to get you in touch with support in your area.
I would comment that with Meniere’s, the use of salt is a known trigger of increased symptoms as well as fatigue, dehydration and at times pressure changes (in my case air pressure, but likely also those experienced during a dive). It would be worth determining whether contact with salt in sea water is strong enough to trigger an attack (on the mouthpiece, etc.) You likely have experienced, the episodes are extremely disorienting with inability to visually focus and are exacerbated by any movement of the head. Often repeated vomiting ensues (not a good idea, I have to suppose, below the surface with oxygen in place.) If you were to snorkel (with others) it would be easier to get attention and assistance if needed).
Each case of Meniere’s can have a different course of progression or remission and regular medical care is important. Other helpful sources of varying levels of knowledge are found on the internet.
Vestibular.org (probably the best resource online and in print for the public with medical and scientific advisors who are key leaders in the field of vestibular medicine and research.
Mdjunction.com (lay forum)
Menieres.org (lay forum)
Numerous sites with suggestions and guidelines for low salt management.
Good luck!