My beloved Persian Stoli did this to us, he stopped eating and he stopped drinking. We took him to the emergency vet clinic, and they got him where he would eat and drink again. Immediately the next morning we took him to the vet, where we discovered the culprit was his kidneys. He was on special medication for the remainder of his life, and he passed on almost two years ago in May of 10.
If you have not, take your cat to his vet as soon as you can. Find out exactly what is wrong, at least they can get some fluid into him by IV if necessary. This is your best bet.