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.
When running with your dog, some of the signs you need to look out for showing they may have over done it are: 1  Starting to fall behind, and slowing down compared to their usual performance. 2  Limping or lameness in any way and to any level of severity. 3  Shortness of breath or excessively panting during the exercise.