After much debate with my doctors and mages, and making him swear a magical vow to not tell anybody of this, I finally told Starswirl I was suffering from these hallucinations and sensations for some time.
Luckily, Starswirl agreed to all of my terms and even the vow. So I took Starswirl to Aquamaris, and I showed him the notes my mages had written with their magic. Nothing else lasts underwater.
Annnd he hasn’t spoken to me since. Damn it to Tartarus. He still pouring over the reports, muttering to himself, having some seaweed that we bring to him, as well as fresh water. Occasionally he exits to pass waste. But he’s ignored all attempts to communicate with him.
Crazy land pony.