Like humans, dogs dream and have nightmares. Like you, your puppy experiences two types of sleep – rapid eye movement sleep or REM and non-REM sleep. Usually, when a puppy enters REM sleep, they have vivid dreams. They start twitching, their eyelids start rapidly moving, and they start whining and breathing rapidly.
If your furry friend is having a nightmare, do not try to wake it up as it may get aggressive and attack you out of fear. If your pooch has recurring nightmares, consult a vet.