I think you should take the cat to the vet ASAP--I've had a lot of cats...and sometimes I think a few of them died cause we didn't act fast enough. Although they got weird, genetic diseases (and in one case cancer from being outside too much), it's best to take them to the vet if you think they're really being weird. At least, down here, we have a lot of lizards, snakes, frogs, etc, and my cat CONSTANTLY tries to eat the fucking things. XD;; So maybe it was something he ate--still, a vet would be able to let you know quickly.