Thank you for your reply Lyn. I did ask him if he thought he had a urine infection, but he doesn't think so. We have some tests here because he had a lot of UTIs before he had treatment for PC, so I will suggest he checks.
No issues with stress (happily retired) or alcohol (he did have a G&T but no more than usual!) and he doesn't take sleeping tablets. He does think he forgot to go to the toilet before we went to bed last night. I did say perhaps he was just in a very deep sleep, but he is shocked that he didn't wake up because he needed the toilet. Amanda