The most common cause of this loss of balance is an inner ear infection or even vestibular disease. Vestibular disease is a problem in the inner ear and it can cause stroke-like symptoms (falling, stumbling, etc).
No matter what, you need to see the vet as soon as you can for an exam and to discuss your treatment options. This could be simple or it could be major.
Mad cow disease is not a concern.
Let me know if you still have questions.
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