Thanks for all your comments on Rupert not being well.
Pleased to say he has eaten a little chicken and had his usual drink from the bathroom sink. He slept okay last night and didn't bother me as he had the night before so I think we can safely say he's turned the corner until the next time.
I have no idea what causes these episodes but they are alarming.
Animals cannot speak and let us know how they feel and after two operations on his bowels I'm sure he probably has scar tissue that maybe plays him up from time to time.
As for your suggestions of diet. We do all we can by only giving all of them special fur ball biscuits and he has a small dribble of lactulose (recommended by the vet) in his evening meal every day, apart from brushing we can do no more.