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.
The symptoms you have described have me concerned. While a puppy can be a little sad because of losing a playmate they would not be this sick. Any time a puppy doesn't want to eat there is usually something wrong. There are a number of things that can cause a puppy to not eat or drink and to stumble when walking. It may be that she is fighting a virus.