Dog Smacks Lips While Sleeping. If your dog is hanging around their food bowl or spending time in the kitchen while smacking their lips, then they are probably just looking to be fed. Why is my cat smacking its lips while sleeping?

Constant smacking or licking of lips can act as an instinctual calming behavior that helps your dog relax, but it. A bout of acid reflux could see them smack their lips in their sleep too. So it's not quite a stress signal as a calming signal when a dog is doing one of those signals in a place where they should be calm (like yawning when in bed or licking it's lips around family) then it just means they are calm and hence doing the signal.