Winston has random "asthma attacks" ... help!

Winston randomly suffers from what are best described as asthma attacks. He will be walking/running on his harness and all of a sudden will stop, his tail gets rigid, he "points" with his body, and he lets out a series of gasping, rattly wheezing noises for between 10 seconds and ~30 seconds.

This seems to be a random occurrence but we have only seen it happen when he is outside and in his harness. The harness is never tight around his neck (I have verified each time it has happened).

He doesn't appear to be overly bothered by it, although his eyes might bulge a little bit and his face may look a bit panicked. Today, he continued walking and running, apparently unconcerned, even while making the noises.

Could he be getting so excited while on the harness (he jumps around and hauls at it pretty hard) that he inadvertently affects his air supply, or am I being an idiot and need to take him to the vet immediately?

This sounds like back snorting. Lots of Cavaliers do this as they have a long pallet. Hold the muzzle and point it downwards. You can also cover the nostrils. The pallet will go back to its right position and the snorting will stop. Dylan does this but he is quite distressed by it, he always funs to me for me to fix it.

You might want to discuss this with your vet if he is having this as a regular problem. The 'snort' is quite common because of their foreshortened muzzles and is almost certainly what you are describing but dogs can actually have serious complications from it and some need corrective surgery. Basically the dog is literally gasping for breath when this happens as part of the airway is obstructed. If he is doing this to the point of discomfort (eg bulging eyes!) I'd have a vet check him over.