If you ate really healthy food for a long period of time and then shocked your system with a really unhealthy wet meal like he did... you'd be pretty ill feeling too! As long as he's drinking and eating, even if its less than normal... he's not feeling 100%... he should bounce back... give him a day or two to recover...
if he gets WORSE instead of better head straight to the vet! But really, it sounds like it was "something he ate"
For me its Pasta with Heavy Cream Sauce! A favorite
... But it takes days to recover!
lol