Dogs have nightmares too

Sometimes I wake up to the moaning of our dog - 2 dogs are sleeping in our bedroom. It is usually Tisoy, the 8-year old spitz who would be moaning and groaning while sleeping. I would wake him up and he would look surprised. But obviously he was having a nightmare. I had consulted the vet about it and she said that she also believes that dogs experience dreams and also nightmares. And for a precaution like humans, we should also waken the dog to stop the nightmare that he is experiencing.