screaming chihuahua

Question
Our 3 year old chihuahua often "burrows" by getting under blankets on our laps durring the day or in bed at night. Recently, when we move him at all while he is burrowed and sleeping he lets out a scream / yelp. It used to be common for him to growl a bit when he was sleeping and we moved him but this is entirely different. When he does this he is clearly frightened after it happens. He runs away to be by himself (not common) and seems very scared... he will not even eat his favorite foods after it happens. The other night he woke me and my wife up just screaming and yelping in bed, this continued for 30 to 45 seconds before he stopped.

We took him to the vet and after a physical exam she said that his knee-cap might be slipping out because it is common in smaller breeds. This seems off to us because this has happened when he is sleeping in many different positions (side, belly, ect). Additionally, he does not even need to be burrowed and sleeping for an extended period of time for this to happen, just a few minutes. He actually just made the noise when my wife shifted her legs while he was laying in her lap.

we have no clue why this is happening and I don't think our vet did either, please advise and thank you.

Answer
He could be at least partially right. It could've started as a problem with his knee and by petting him, reassuring him and offering him treats when it happens you are reinforcing the behavior. It could also be something as simple as a toenail getting hung, or as complicated as the kneecap. My first suggestion would be to take him to a different vet for a second opinion, meanwhile, ignore his behavior as much as possible. Don't respond AT ALL, and see if he doesn't improve within a week or so.
Cindi