I don't know if you have found this, but never argue or try to reason with them. Just agree and then try and distract them. Move on to something else. It was a suggestion from my son. I have tried it and it works, at least for us.Thanks Heartbeat.
It can be hard especially when they pick up on something and get totally the wrong meaning from it or completely misinterpret it but no matter what you say they still keep going back to the misinterpretation. I Can't say I've found the answer of successfully dealing with it.
I know what you mean regarding 'get well soon', most illnesses there is some hope that someone can get well again but it's not likely a cure for dementia will be found in time for our OH's. We can just try and make the best of things and make some good memories whilst we can and for the bad times try and deal with them as they arise.