Kitty moves really slowly, no meowing, not eating or drinking

My 5 year old shorthair (Hex) has been acting strangely for barely 3 days. But as each day passes his condition has drastically gotten worse.

We found some stale gucky water that him and the other cat in the house were drinking from, for what I guess was only a day or so. Around then, we found a lot of throw up, some with dry cat food in it (we suspected it was from the other cat, who is now healthy), and some that just looked like bile. We immediately changed back the diet from dry to wet just in case.

Now, as the other cat has shown no symptoms, we have noticed Hex has almost completely changed in terms of behavior. He now walks and moves extremely slowly, showing a bit of discharge around his eyes, he never meows (he's a big talker), doesn't snuggle and hides most of the time, and hasn't had any food or water from what we have noticed. We gave him some water through a syringe, but he didn't take to it much.

We can't get him to a vet until Friday, does anyone have any suggestions as to what might be going on, and how we can make him as comfortable as possible until we can get him properly checked out?

Something appears to be majorly wrong and I would consider this an emergency.  If you can get him to the vet sooner, please do.  I just went through the same symptoms with my male cat - extremely lethargic, vomiting bile, not eating, not drinking, moving slowly, would lay down wherever I put him..  Turns out he ate a rubber door stop.  I didn't get him treated for 3 days.  Had I waited even one more day to take him in, he wouldn't have made it.

It could be poisoning, a foreign body ingested, or illness.  Either way, the longer you wait, the worse he is going to get.  Please let your vet know that its an emergency.

The other problem is the lack of eating which will cause hepatic lipidosis fairly quickly.  This will require a feeding tube (more $$).  I'm not trying to scare you, but I just went through this same situation not one month ago and the sooner you take action the better.