I remember when my mum told me she had been diagnosed with Microscopic Polyangitis, my first question was "What the hell is that!?"
I definitely didn't mean "Do you have any reading materials or literature that you can refer me to because I want/need all the details of your health condition".
What I meant was: can you give me a rough overview in a few short sentences, and tell me any key details (eg. she needed chemo, or else she was going to lose her kidney function...how that works precisely? Is still a mystery to me - I don't need to understand that kind of detail to support her, and frankly, I wouldn't understand even if she tried to explain it, or had excellent literature that she could refer me to, because, having Googled it, it's pretty complicated).
I take much the same approach when telling people about my ptsd. They don't want, or need, much information. Microscopic polyangitis is a complex condition that can impact many of the body's organs, but for my mum? The big impact of the condition on her personally was that (a) it was impacting her kidney function the most, and that was really serious; and (b) she needed chemo for it, which having told me about, I could help get her through it. Realistically, I ended up needing to know more about chemotherapy than the illness she had.
There's a whole heap about ptsd that doesn't impact me much. There's some things that impact me a lot. There's some things that it's helpful for certain people in my life to know about. So when I tell someone I have ptsd, I base what I'm telling them on "What do I want them to do with this information?"
For example, I told my boxing instructor "I have ptsd, so I have reeeeally bad concentration". I need him to know that, so that when we're training, he keeps the instructions short and simple, and repeats them regularly. I haven't bothered to explain that it's because I dissociate. He doesn't know what dissociation is, and tbh, he doesn't need to know, nor does he need to care.
With my mum? "I have ptsd, so I find places like shopping centres too stressful to deal with". Because I need her to know that when I catch up with her, we can go to the local nursery to pick out plants, but we can't go to the shopping centre for lunch. There's overlapping reasons I can't go to shopping centres, which aren't relevant, and which I can't succinctly explain. The important thing for my mum to know? Is simply that I can't do shopping centres.
If I tell someone and they want to know more? They'll google it. They really will. That's how people get their info on stuff they're curious about. If they're sensible? They'll visit websites of reliable mental health information (which are abundant, and summarise ptsd far better than I ever will!!).
So, for me, what I tell someone is always about "What do I want them to do with this information?" That makes it pretty easy for me to navigate what I tell them, and if I can't think of anything that I want them to do with the information? Then most likely they don't need to know.