why does my dog wake up suddenly, fearful

Vinny is a 5yr old Frenchie. about 3 months ago he was napping and suddenly woke up startled, scared, yelping, couldn’t figure out where to run first and emitting the oil gland smell. He has done this several times a day since, only 1 other time with the smell and not always as severe with the crying. but he is definitely scared and wants to get up close to my husband or me for comfort. we’ve checked him over for bone pain and he seems to be fine. his vet check ups are great last one was last week. vinny was stolen from the litter at 6 wks when we got him back his ears had been cropped like a pit bulls or dobies, short and pointy. is it possible he’s having nightmares of those times. its so sad especially when he cries. its so distressing. hope you can help and thank you for your wonderful program and commitment to mans best friend.