Is my Oscar fish sick or is this normal?

I have an albino tiger oscar who i believe ate one of the baby Electric yellow mbuna cichlids because there were three of them and now there are two. Anyway i don't think it was sick because i had it for about 3 weeks in a different tank until i got bigger and then i put it in, but ever since the oscar (5-6") has been hiding in the corner of the tank behind all the ornaments and he hasn't eaten anything for a while, and he seems frightened every time someone swims by. what is the problem. Also hes in a 55g tank i feed him hikari gold pellets, crickets, blood worms, and occasionally meal worms.