No advice on what more to check than you already have, but I wanted to say that Sweep had a cut/abrasion on her tongue after one of her surgeries. She must have bitten it in her zonked-out state or it was from her intubation. We gave her Manuka honey a couple times a day, which she was totally on board with, and it healed up quickly.
Hope it's nothing and Mark is good as new soon!