Because depression is a chemical imbalance. Some people, such as myself, have to take medication to get some sort of mood stability. You might be one of those people too. I know side effects suck, but you'll feel better once you are medicated right. Also sometimes, side effects go away. You see, I am on Tegretol, and for a while it gave me blurry vision in only my right eye, but that went away. It might be the same way with your "feeling stupid", so just give it some time.