You need to take your dog to the vet and have it properly diagnosed and treated. We cannot diagnose your dog over the Internet. It could be seizures, he could have gotten into something he should not have. The list is endless of what it could be. If this has been going on for 12 hours straight with no signs of stopping, you need to get off the computer and take him to a vet NOW. Please do not allow this to go on any longer than it already has.