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I would switch him over to a bland diet of jarred baby food for the next few days. Just be sure to get a brand with no garlic and no onions. You can also use boiled chicken and white rice made at home. Give this in small amounts several times a day. Never let his stomach get empty. You can use a little hairball remedy to coat the throat and this will help with any reflux.
If this does not start to resolve, you should see your vet.
Let me know if you still have questions.
You should be very worried. Any time that a cat won't eat for more than 48 hours, you are in serious trouble. Their liver can fail and then the cat can die. It is called hepatic lipidosis where the liver thinks it is being starved and starts "grabbing" fat cells...and actually ends up killing the liver.
I suggest that you see the vet first thing tomorrow for a full exam and possibly bloodwork to find out what's going on.