There could be a few causes for these symptoms. The most common cause of disorientation, falling, stumbling, etc, in n dog is vestibular disease, a disease of the inner ear. It can even cause stroke like symptoms with one sided weakness, facial paralysis and drooling.
There are other potential problems but this is the most common.
I do suggest that you go ahead and see the vet with him as soon as you can because time is important to treatment.
Let me know if you still have questions.