It's a pain being allergic to cats. We were invited to eat at the home of some friends in the church on Sunday and they have a very friendly, very furry cat who loves to be stroked etc...
We ate very well and were very happy, but I was getting more and more clogged up and asthmatic, so we had to leave.
The problem is that if you explain why, then either people feel guilty for having a cat (!) or they think that perhaps if they put the cat out all will be OK (it won't - it isn't presence of cat that sets you off, it's essence of cat and that takes weeks to clear.) Meanwhile you feel too uncomfortable and short of breath to discuss it !
So it's better to make some kind of excuse and leave, then to let them know later when you are able to explain without feeling ill and distressed !
It also meant that preaching was a bit bizarre as I needed to have tissues handy to blow my nose and also explain why from time to time I had to stop and stifle sneezes !