Well, my poor old cat Fluff has got cystitis again. Our vet has given him another dose of antibiotics and will check him again in a couple of days. He seems much better today but apparently it can be dangerous in male cats as the urethra can become blocked. Trying to keep calm. This information online is not very cheering though:
Why do cats get cystitis?
There are a number of possible causes of cystitis, but the majority of young cats which develop cystitis do so as a result of stress. Sometimes an obvious reason for the underlying stress can be identified, such as the house being decorated or another cat or a dog moving in, but often it is difficult to recognise the actual cause of the stress. Once cats have developed this type of cystitis, they are very prone to having further bouts of it in the future and in some cases management of some variety is necessary to prevent further episodes.
A smaller proportion of cats, especially elderly individuals or those with chronic problems, such as kidney disease, develop cystitis due to infection, generally by bacteria.