My Yellow Clown Goby didn't move or eat for 3 days.. and i was worrying just like you are now. 3 to 4 days later.. he chases down food and now explores my tank. Like i said before, don't expect anything to happen with the first week of having the fish, maybe even a bit longer. You need to give them time to adjust. If it's 2 - 3 weeks down the road and he still won't move much or eat.. then you can start worrying. But by then, it might be already dead lol.. if it hasn't eaten for 2 weeks i don't think it would be doing that good.
Just give it time.