My dog has seizures. He does drool and foam at the mouth during a seizure. A grand mal seizure can make an dog expend as much energy as he would running a marathon. It is exhausting for them. If there was one or more seizure the dog could be exhausted and lathargic for a day or two. He probably had a seizure, but you need to find the cause. The fence digging could be part of a seizure. Dogs sometimes become obsessive compulsive during smaller focal seizures. They act confused and paranoid. They can dig, eat dirt, run in circles, snap at imaginary flies, continually try to run or escape from imaginary demons, etc. Mine tries to eat the carpet, the grass, dirt or anything under his feet. Your dog may have eaten something, have a disease, have a genetic disorder, or be reacting to shots, flea applications or heartworm tablets. If you want to save the dog, you can't wait to take him to the vet. If your vet can't see him, find a farm vet. They are usually cheaper.