Kosh has had chest X-rays to see whether his breathing was due to some underlying lung problem, and it appears not. However, he's apparently not taking food, and so bellinghwoman is just popping round to the vet with a tin of his usual cat food, to see if that will tempt him.
Thanks to all who've expressed their concerns. He's coming up 14, but has had (apart from the long term skin complaint) generally good health. So we hope this is just a scare.