Neck Swelling from Drool

I have an English Mastiff that just underwent surgery for a portion of his tail that was amputated. He is currently staying at our Veterinary for his recovery. He is wearing a cone to keep from chewing at his stitches, but his neck has swelled up to twice the size in a couple of days. It also smells like dead fish. The doctor blames it on the dogs drool and claims they are washing his neck daily with a special shampoo, but my dog seems uncomfortable and would not take a dog treat. It does not seem likely that his neck would swell to this size due to his neck being damp. Is he in danger of suffocation, and is this common for this type of situation?