Retaining water, swelling up, not righting himself, muscle spasms, all those things sound like calcium deficiency in later stages. Liquid calcium by syringe is usually how that's treated. This website seems to suggest that: http://www.repticzone.com/forums/Tre...s/1125949.html

But it could also be chytrid if you could check the underside of his legs for redness that might help.

Or it could be a response to something toxic.

Big disclaimer: I'm not a vet. If possible you need to see one as soon as possible.