I am sorry to hear you are worried about your dog. I am a veterinarian, and will do my best to help.
When dogs suddenly act different, or anxious, it can be a sign of internal disease, or pain. SInce she is shaking her head, that is another clue. She could have something in an ear
, and ear infection, or neck pain.
Is she eating and drinking normally? Any vomiting or diarrhea?
She is trying to tell you something, and putting her head back and shaking her head make me think the problem is in her head, neck, or ears. If she were mine, I would start with a good physical examination as well as looking in her ears with an otoscope. When you look in the ears without a scope, you can only see about 1/4th of the ear canal; to see the whole canal and the ear drum you need a scope.
Let me know how she is doing and what else I can answer.