We have three cats who are all littermates and usually get along well. I had to take my one boy into the vet on Thursday because he was vomiting and dehydrated. When I got back from the vet, the other male started hissy and striking at him. It is now the third day and this is still occuring. In the past this type of behavior only lasted 24 hours max after a vet visit. The agressive male is actually charging at the other cat. The cat that went to the vet is the more docile of the two. I am worried that this might become permanent. The hissy kitty is even hissing at me.