My dog is makin weird sounds!?!?

Well I'm watching tv and it's like 11 or 12 at the time so ya it's nite. I randomly start hearing sound like someone's gulping soda or somthing and i realize it's coming from my dog. Specifically her torso and her stomach is like quivering so i pet her. And she like freaks and wakes up and then once she sees it's me she relaxes. Same thing happened like 5 min. Later wen she's on the couch, so I pet her and she like freaks out. I think maybe she's dreaming and it a nightmare but I'm not sure. Can dogs dream and have nightmares? And wat do u think is wrong with my dog? She's just a lil cockapoo so it's scary to see that happen...