Fussing while sleeping

Does anyone's baby fuss while they're sleeping? My LO will be fast asleep but will start to fuss about something, I'm trying to figure out what it is. She does have reflux, but that typically wakes her up, and has been better since we elevated her basinett pad more than it was before. If it was a dirty diaper she'd wake up too, but we've been using the overnight diapers which have helped with those middle of the night changes. I'm kind of stumped since it's not an obvious issue, but she's fussing about something