I have 2 male cats that lived together for a long time and they just now started fighting for no reason?

Cat #1 recently threw up to the point of bile. since then cat #2 goes after him and seemingly wants to kill him. this is not a play fight and these cats have been together for at least 6 years (they are my wifes and she had them before we met). This has never happened before like this. Cat #2 gets a poofy tail and does a hollow meow and cat #1 growls and hisses. They do not attack the other two cats. Ages are 5 and 6 approx.