I wouldn't worry too much. As he comes out of brumation, just feed him a little extra protein and lots of veggies. Also make sure you supplement him correctly and he should put all the weight on that he lost before, plus some. :lol:
I know my guy weighed 520g before he went into brumation, and when he came out he was down to 460g. He's now up to 543g. It's ok to be paranoid about their weights and such because then you notice when something really is wrong and you can get a jump on it faster. :wink: