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.
Sudden turns may cause the ataxic dog to stumble. A tenancy to lose their balance is also apparent when a dog with ataxia makes a sudden turn. Sudden head movements, such as shaking the head, may precipitate a dizzy spell that will cause the dog to lose their balance, stretch out their legs, and fall to the ground.