Does anyone know why my dog is breathing like this?

Background: got him as a rescue about 2 months ago and all I know is that he came from a hoarding situation and is around 6 years old. No known medical conditions or history. He had bad fur/skin when I got him so I give him omega 3 daily and he is fed Authority wet and dry food with fresh fruit or veggies daily. He's also current on all vaccines.Since I got him (idk if it happened before I got him but the rescue didn't mention it) hell occasionally have sneezing or a little cough. The cough is like... Coughing a couple of times with a little gag at the end but nothing ever comes up. A couple of weeks ago I woke up in the middle of the night to him doing this horrible sounding cough. It was similar to what is linked below, but seemed a little worse with gagging and heavier inhales. Wasn't able to catch it on video but I freaked out and went to the emergency vet (I was supposed to leave at 7am to drive to my family's house 8 hours away and they have dogs, I didn't want to risk his health or my parents dogs health).The vet said he sounded fine, hadn't done coughing or wheezing since being there. Vitals were all fine as was heart and lungs. His eating, potty and play habits also hadn't changed so the vet brushed it off as just a coughing fit or something.I understand if that's the case, however this happened again twice tonight and I'm just wondering what may be causing it. Does it seem (or sound?) like allergies? He doesn't have any other signs of a resp infection or anything major so I don't really know what else it is or how to help him. He woke up from a sleep and started doing this. Could it be asthma?https://ift.tt/2IiLAeh via /r/AskVet https://ift.tt/2GMygOH