Being an amputee means I constantly have people staring at me or that I can't go out in public without someone asking me "what happened?" This post is a quick FYI on when I think it is or isn't appropriate to ask a disabled person "what happened?" (Note this is my personal account and others may have different feelings). Being out and trying to get on with my life, whether I'm doing groceries or at a bar with friends shouldn't include me recounting the most difficult, physically and emotionally exhausting time in my life. I'd equate it to walking up to a stranger and saying "Hey, tell me about the worst time of your life." Or "hey do you mind running through your medical history real quick." Keyword here is stranger. I like to be able to share things with friends and my friends should know what happened to me in the way that friendships begin and people get to know each other. What I don't like is a stranger feeling entitled to personal info just because my condition is visible.
I also think it's ok if it's in context. Such as a back and forward conversation about such conditions or if I bring it up first, which is an indication that I'm ok with sharing such details with that person.
In short, don't walk up to a person with a disability just to ask them to recount what happened to them in order to fill your curiosity. Who they are is more important than what happened to them.