Pics of the setup? Give him a substrate he can burrow in if he's not already. I assume you've double checked your temps, ambient and hot spot with a temp gun? You said temp is 85, is that the hot spot or all over? I keep mine around 77-81 ambient and then with a little warmer on the hot spot. He hasn't been off feed long, but I'm wondering how long you have had him and what the feeding schedule was before, if he was eating well for months I'd expect him to be quite a bit heavier.