The border traverses a variety of terrains, ranging from major urban areas to uninhabitable deserts. Approximately 350 million legal crossings occur annually, and is the most frequently crossed border in the world. The total length of the continental border is 1,954 miles (3,145 km).
Only a veterinarian will know what's wrong with your dog but usually stumbling, wobbling and falling down is associated with neurological problems, especially if there aren't any other signs. I would really take him to the vet as soon as you can.
My dog is stumbling and wobbling when he moves. This morning he was fine but I just went to feed him a few minutes ago and he got up and immediately I noticed he couldn't keep his balance. He was stumbling and wobbling back and forth but appeared to be full of energy.