No, Max hasn't put on a bit of weight.
He was looking a bit off last weekend, and then started moving sort of stiffly, and when I came in from work on Monday he looked not at all well.....so off to the vet, who found that he had a temperature and a rather full bladder; he was not a well cat. We were kept up to date with any progress in his condition by phone, and on Friday afternoon, the vet rang to say that he was ready to come home, and that the problem was cystitis - he had responded very well to treatment, and certainly looked much better. We now have a few days of tablets to deal with, and have to keep him indoors until Monday to make sure he's pissing properly, then back to the vet for a quick check on the state of his bladder, and that's it, hopefully.
Total damage, including scans, blood tests, lots of drugs and 3 nights B&B - £816 (inc VAT), plus about £60 in taxi fares.
We have pet insurance (with Tesco), but without it, we'd be stuffed.
Think on't.