This happens in Germany.
Work culture doesn’t fit my personality: I don’t talk much, I keep to myself, I simply want to do my job and go home, I separate my personal life from work, my colleagues are full fledged gossips, ignore the duties that need to be done and then expect me to help them when they are late. I don’t have patience for that crap anymore.
Due to internal regulations, I have to stay on the unit for 4 weeks after sending my notice. Answering honestly the question of why I’m quitting would ensure that they yell at me and bully me, and I don’t want to experience that again. Even saying ‘it’s none of your business’ ensures that they feel insulted and start yelling. I have decided I don’t have patience for people like that anymore.
So, what do I say?
Not at all.
If someone asks another person close to OP about their “medical issue” and the other person is clueless, there’s a way out.
Say they’re confronted by an old coworker later down the line who says “I talked to your sister/mother/SO/best friend/whatever and they said that you don’t have any medical issues!”
Then OP simply acts upset and says “you told × about my private medical issue???” and act distressed over it.
However, I doubt these coworkers care about follow-up. So this situation is very unlikely to occur.
Private medical issue = private. Even people close may not know. It’s a good alibi.