I'm so sorry to read that your little boy is in so much discomfort. I'm not sure that I am able to help at all but I just want to say that I am thinking of you & Harry.
It is difficult to be quite sure what is happening from your description, but it does sound as if he is having difficulty breathing.
I know he had severe MVD symptoms last year. Perhaps an urgent referral to a Cardiologist or has he recently been seen by one already?
I'm not sure about the vomiting. I have not experienced that symptom with my MVD cavaliers and I would have thought vomiting bile was more due to digestive problems or stomach irritation.
It could be a side effect of the long term heart drugs I suppose.
Please let us know how he is doing.
Cavaliers......Faith, The Ginger Tank and Woody.
Japanese Chins.... Dandy, Benny, Bridgette and Hana.
Remembered with love......... Tommy Tuppence and Fonzi