Daisy, I'm sorry about your cat. We had almost the exact same situation in June, our cat suddenly developed trouble breathing and died as soon as we arrived at the ER vet. I felt terribly guilty.

Now our 5 year old cat is in the hospital with liver trouble (perhaps Fatty Liver Disease). She is not doing well and we have spent a boatload on vet bills. The vet called today with an update and said it was too soon to know if she was going to recover or not and that we should take it day by day.