Bi-polar cat?

OK, here is a bit of a story.
Runt is a two year old neutered tom. Piggy is his sister. Late last year, Runt started attacking Piggy occasionaly. He would get put in "time-out" every time it would occur. In between the chase/attacks, they would cuddle and get along fine. Then, Runt started attacking the big dogs as well. They would run and try to hide behind us. Piggy started helping him with the dog attacks. Runt was still doing his Piggy attacks, as well. Now, he has begun hyper-grooming to the point of bald patches on his legs and tummy. The vet has put him on kitty Prozac, but the full effects won't be seen for at least a month, yet.
I would blame last year's move, or this year's new puppy; but the behavior changes didn't occur any where near these events. Does anyone have any ideas on how to help Piggy, the big dogs, and Runt's fur? Thanks.

I suppose that as with some humans mental illness is entirely chemically based - as in, the brain chemistry is off in some way, it could be the case with him, too.

One woman I know was a paranoid schizophrenic, and for a time, they were able to find a medication that balanced out certain brain chemistry and she was fine, but if she missed a dose, it was all over because then the paranoia would kick in and she'd see the medication as a plot to "get" her. It was sad, but just something about how her own brain chemistry. I hope the Prozac helps Runt. I wouldn't call his behavior Bi-polar, though, it seems much more random than that. Are there any indicators of when he's about to "go off?"

I truly don't think of him as bi-polar, either. It was just the easiest way to describe his behaviour. I have not had the opportunity to observe him just before an attack; just during and after. As far as I can tell, though, none of the attacks have been provoked by the attackees.
He has never been aggressive towards us, is very sweet with all the other cats (grooms and cuddles), and is actually a big cuddle-bug most of the time. He IS extremely competitive when we play with the feather wands.
Hopefully, the medicine will help.

My Diego is on kitty prozac. His anxiety issues led to him stalking and attacking his sister. The first dose of 3.5 mg worked but only for a short period of time. He's now on 5 mg, taken as salmon flavored chews. He takes it like a treat and is a lovely boy to be around again.