Do you have alot of decoration in your tank? I noticed some of my frogs burrowed themselves alot, but when I added plants and leaves, they started staying up more.
Frogs don't hibernate unless they are too cold or too dry, if your readings are correct, he shouldn't be hibernating. My advice would be to dig him up and give him a lukewarm dechlorinated bath for 30 minutes, then put him back and try feeding him.
Always kill prey like rodents, never take chances with your frogs health, all it takes is one wrong grab to lose an eye.