Teeth Grinding and possibly weight loss???

I just got anot her chin, he's 8 years old and his name is Lou. He's normally very friendly and quiet, but today I walked in and I heard some awful teeth grinding. It was like nails on a chalkboard. I thought it was my other chin Loki at first but when I looked I realized it was my 8 year old. As I examined him it almost seemed like his little hip bones were sticking out a little more.... or maybe I'm panicking, I'm not sure. He just seems a bit out of it, if you will... Possibly Thinner? Yet when I offered him a papaya and a nut he was very quick to take the nut from me but strangely refused the papaya. I'm worried about him but he isn't showing any other signs like drooling or watery eyes or nose or lying on his side. Any suggestions from anyone who's experienced simular situations/symptoms? Let me know...

Thanks

Mande