My dogs behavior is off-he keeps attacking my cat like he doesnt know who she is.

Question
Hi, my Jack Russell Terrier mix dog, who is one, keeps attacking and terrorizing my 4 year old cat. He always does this, BUT it's not playful like normal. The way he barks at her makes it seem like he doesn't recognize her and that she is some threat to him. It just started on Sunday night, and it's happened 3 times now. He chases after her and completely scares her but he's rough and not gentle. It's really worrying me and I don't know what to do. Thanks.

Answer
Has this dog been raised with this cat? Have you noticed any change in behavior of the cat (possible illness, not eating/drinking, change in litter box behavior, difficulty breathing, etc.)?  What is the cat doing when the dog behaves in this manner?  I need more information.