Regardless of the exact physiological mechanism, I'd boil my incident statement down to this:
"Student performed a CESA in the middle of Open Water dive #4. After resting on the surface for a very brief time (< 30 sec), on subsequent descent, the student reported experiencing a mental fogginess and dreamlike/euphoric state, and hearing "tones" in his right ear. The "mental fogginess" lead to the student botching equalization on the descent, with a forced Valsalva maneuver, and subsequently suffering inner ear barotrauma (as diagnosed by an ENT 4 days post-incident.) The student lost nearly 100% of his hearing in the right ear; ~2 months post-incident, the student has recovered ~50% of his hearing, with some persistent hearing loss and tinnitus. Treatment consisted of prednisone (oral steroids), 9 intratympanic steroids, and hyperbaric oxygen treatments."
I hope that is of some benefit to other divers. (I've reported this to both PADI and DAN.)
Ken, I'm going to recommend merging the thread you started for the same issue in mid-March with this one so information can be consolidated.
Best regards,
DDM