I believe this is right. When there is a change in a multi-cat household, ie a new addition, a new hierarchy has to be established. There can be a few hissing matches before everyone finds their place again. There are many people who will never interfere with this, but I am a bit of a wimp about biting, and I would also use a water pistol if it got a bit much. Toby maybe needs lots of your attention to reassure him - that is if you are up to it. Are you feeling any better?