Re: Sudden aggressive behavior?
Welcome, and I'm sorry your kitty is pulling a Jekyll/Hyde routine on you, it must be scary. Most cats are reactive to the environment around them and smells/odors are a very big part of how they perceive their world. There is a behavior called "re-directed or mis-directed aggression", where something (sight, sound, smell) triggers a cat to get angry/defensive and they become frustrated when they either cannot locate or reach the source of their animosity so they direct it to the nearest victim, which usually happens to be other household pets but can include the people of the family, too.
Have you noticed her behaving in this manner after you've been outside? Handled other animals or anything that smells differently than your household? I know it is most often experienced after a stray cat has been seen outside in the yard, a new/different animal has been handled and/or another household pet has had to visit the vet and comes home smelling of the vet office. Sometimes, people are successful in combating this behavior by seperating the cats and applying a drop of vanilla to the back of the neck of each animal. This helps to sort of 'overwhelm' their sense of smell and make everything smell the same, which is soothing for the animals, because when something smells different, it can sometimes be perceived instinctually as a danger, and this is why many pets act so aggressively.
I would also like to caution you against approaching your cat when she is in the thrall of one of these episodes because she will react instinctively and may harm you. This is a normal behavior, but because the cat is being governed by their instincts, the cat won't 'behave as normal' in the way we perceive the cat's everyday behavior. The key is to try to find what is triggering this reaction in the cat and remove that trigger.
Best of luck,