What happens when you stop taking anastrozole?

I've been taking anastrozole for six months to shrink tumors in preparation for surgery. I stopped taking it about a week and a half ago as the doctor ordered since my surgery is coming up. I've felt weird and not very well since stopping. I've been tired, kind of dizzy, and just not feeling myself. Anyone have experience with side effects when stopping Anastrozole? Thank you. I go back on it after surgery.