During this attack he clutches his mouth tight and his hands and legs become stiff. We massage him when something like this happens. This remains for 10 to 15 minutes and then he becomes absolutely normal.

It sounds like a seizure. You should take your dog to the vet - they will probably want to do some diagnostics to figure out what caused it.

I agree with Saris about the seizures. Once the vet has done some testing they will be able to give you medication and tips on stopping the seizures. For some dogs it's diet, others need medications.