To me it looks like his mantle has collapsed causing him difficulties to stand up. I've seen it a few times on my snails. If it is his mantle there sadly isn't anything you can do for him. How is he now?
70 gallon elephant nose tank, Gonzo the elephant nose and friends!
30gallon borara merah and brigittae green, red longfin bristlenose, shrimp, ninja, taiwan,bamboo, and snails.