Ralph mate I'm sure its very scary for you, but as a childhood asthma sufferer let me tell you its a lot more scary for him. You did the exactly the right thing to try to calm him and help him to breathe - a hard thing for a scared youngster.
I had several stays in hospital, one which meant I missed an entire half term of school in year 5 (I think - I'm crap with these new fangled school years!). I was not in good shape and scared the crap out of my parents more than once. The point is I got over it and have enjoyed sport since my early teens, I'm sure your son will too.
In the meantime, group hug time!
Thoughts with you and your family in this difficult time.