Last year a group of 5 friends and I were off on holiday. Sitting excitedly on the plane, I couldn’t help noticing my (usually) very composed friend wriggling in her seat, appearing very anxious and looking over her shoulder. 15 minutes later a ‘ping’ informed us the seat belt signs had come off, but before I could get up to see what was bothering my friend; she was off down the aisle of the plane, into the toilet. Upset stomach? Nerves? Nausea? No, it was a flare-up of cystitis.

Cyst...