I think he may have just ate something that has made the poor little guy sick or that maybe it's a hairball. I know when my cat has a hairball, he lays around a lot, feeling bad and only wants to get up to eat drink or throw up. I can tell you from first hand experience that it is almost always a very very unpleasant smell. The fact is though, we aren't vets and while we can give you our thoughts on the subject, we are not qualified to make a diagnosis. Basicly, what I'm trying to say is that we are all just guessing. I do think that he can wait until Monday to be seen by a vet. That is, as long as he is drinking water and the symptoms don't get worse in some way. So my long winded advice is if he gets worse take him to the emergency vet, if he stays the same, take him to your regular vet Monday, if he gets better, then I would skip the vet altogether. Hope your kitty gets better super fast. Please keep us updated.