you could have pulled a muscle as you slept, but if you workout or do physical labor sometimes you dont know when youve pulled a muscle until you wake up because the healing process cant fix something like that overnight so it will leave you in pain when you were not originally. perhaps your body knew you would be in pain when the dog showed up and you became actually in pain as the threat of the dog became real, then the bite. perhaps that was a polite way of your body warning you, you will be in pain when you wake up so that you dont accidentally push yourself too hard or get confused by the pain.