She was coughing yesterday morning, just occasionally - a big cough every half hour or so. When I got in yesterday afternoon she was still coughing and also sounded sort of 'wet' when she purred. I rang the vet and got an appointment for this afternoon.
Late last night she was on my lap, gave a big hack and spat out a tiny gob of chewed up manky grass onto my t-shirt.
I went to bed worried, and got up to check on her a couple of times in the night, even though I haven't heard her cough since last night. She's over the road on the neighbours wall now, sunning herself and looking very contented.
Blardy animals. 
Debating whether to take her to the vet - I think I might anyway, just to check her out.