Keeping private medical issues PRIVATE

I have few medical issues that are relatively serious and chronic. I am a very private person on many levels and don't like sharing this info with most people. I strongly dislike the feeling that anyone sees or treats me differently because of it. Plus, it's not necessary for anyone to know besides my doctors and me. It's rarely discussed much with anyone, parents included, because I'm pretty sure they know it's a sensitive issue for me.

My dad has company over dinner, a few male friends that I know and see pretty often, and I just heard him tell the whole long story about what happened, my diagnosis, the medical condition itself, etc. He didn't know I could hear.

It's made me super angry and upset. I don't feel like it's ok for my parents to discuss my health issues with whoever the fuck they feel like. I'm 26, if it matters. I HATE knowing that people know but don't know that I know and I can tell they look at me a bit differently sometimes and it makes me want to be a hermit and avoid these people forever.

I sent him a text message he hasn't read yet that told him to shut the fuck up about my health issues. How do I make it totally clear that this isn't something for them to talk about with people, even when I'm not there?

Thanks, XX.