It does sound like a seizure, and contrary to how awful it looks, seizures are not painful. It's also not uncommon for older dogs to develop seizure activity. Call your vet and have him make a note of the episode in your dogs's chart. Make sure you tell him the time of day the seizure happened as well. It may be a one-time occurrence - or not. If the seizures become more commonplace, phenobarbitol is one medication that most vets start with to control them. The key is to document the timing when they happen. I had an old dog who had one known seizure when he turned 12, and that was it. If he had any others it was out of our sight, and that was the end of it. Hopefully that's what your experience will be as well. :-)
Thanks for taking the time to comment! It really eased my fears. I'm glad to know that they are not painful. He just looked like he was in lots of pain with his muscles tightening so much. We called the vet and they wanted us to bring him in. My husband asked what they could do, and they told him that they could put him on medication. My husband wants to just watch him and if it happens again, we will take him right in. Thanks again!