My 10 year old chow started panting and drinking lots of water tonight. He is in excellent health with all up-to-date shots. He has never done this before. He paced and is up and down but constantly panting and breathing short and shallow. It is the wee hours of the morning, so I can't take him to a vet yet. He is not whining, but acts if something is wrong. Please advise

It is hard to say what it is. You are correct about getting him to a vet, or a least talking to the vet. I hope yours has Saturday hours. Mine doesn't.