It's normal for your dog to twitch during his sleep. Dogs dream just as people do, and the result is twitching, vocalizations, and noises.
Canine Seizures - Whole Dog Journal
Do Dogs Dream? Understanding Dog Behaviour
What Do Dogs Dream About When They Bark, Twitch & Cry?
Does My Dog Sleep Too Much? Here's What to Know
Dog in Pain: 12 Signs and What You Can Do to Help - Whole Dog Journal
Why does my dog shake in his sleep?
Why Is My Dog Shaking? Doggy Behaviour 101
Can Dogs Sleep With Their Eyes Open? Strange Behavior Explained
Why Do Dogs Run In Their Sleep?
11 Dog Sleeping Positions: What Do They Mean?