As previously mentioned, it may be due to an allergic reaction that is causing severe irritation of the skin. Your dog might be scratching because he is uncomfortable. By the same token, he may be digging for the same reason. When a person is uncomfortable because of a rash or something similar, that individual tends to be restless. It's hard to get someone in this state to be still and rest. It's not really that much different for your dog. Unfortunately, unexplained and sudden digging could also signal something more serious with your dog's health. If you don't know the reason, consider making an appointment with your veterinarian right away so you can get to the bottom of things. Hopefully, you'll be able to rule out a medical cause for the issue.