i'm not an expert, but here are my $.02:
1) i'd recommend a vet visit, to rule out a physical/chemical change in your kitty.
2) is it possible that he and your other cats got into a "fight" (possibly rough play or a real "get away from me, you're bothering me type")? there's always one cat in the household that is dominant. it's possible he got roughed up and is now afraid of the other cats. you might try separating them for a couple of days, and then introduce them again, slowly, with you there to supervise.