my dog stopped breathing

Question
My dog was barking, then started to clear his throat when he suddenly stopped breathing, his tongue turned blue and he lost control of his bowels.  My boyfriend gave him month-to-mouth and rushed him to the vet's where they put him on oxygen and an IV. His blood pressure and heart rate were low as well. There was nothing stuck in his airway. He eventually came around in 10-20 minutes. The vet could not find anything wrong with him. What could have caused this episode?

Answer
I don't know how old your dog is, but older dogs, like people, get a looser and flappy epiglottis and that can get stuck on a dog's trachea perfectly suffocating them.

There are many other reasons that this can happen such as heart problems etc.
I would say that your dog needs a good work up and exam.
Keep rawhide treats away from him also as these have been known to block the trachea and dogs die from them.

Another thing called syncope (cough drop) can be the result of an underlying issue, usually related to heart problems. Make sure your dog is tested for heartworms also.