My cat has a URI now she has started to loose here balance when she walks, stands up to try and eat. Is this o?

My cat has a really bad head cold and now she has began to start to fall over (loose balance) if she trys to get up is this a symptom of a URI?? Ive been giving her antibiotics she hardly eats anymore i thought maybe the falling over would be because she is really weak but now she is geting more strength and she still is loosing her balance. what can cause a cat to loose there balance?