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 readily suffer from common illnesses and this may cause them to faint. If your dog collapses, you should take him to the nearest vet immediately. The longer you delay the visit, the worse will be the repercussions. Lastly, another reason which may lead the dog to collapse is simply because of the loss of stability or balance. In this regard, the dog can easily lose gait and fall over. This loss of balance may be related to certain infections of the ears or the worse if it relates to a more serious problem which includes the disruption of the control center for balance, which is located in the brain.