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.
Dogs can fall to the side and make paddling motions with their legs. They sometimes poop or pee during the seizure. Some dogs may look dazed, seem unsteady or confused, or stare off into space before a seizure. Afterward, your dog may be disoriented, wobbly, or temporarily blind.