Personally I have no problem providing evidence of my conditions, it seems to be more of an American thing? I get things are personal to people but sometimes in life if you want something there's a price to pay.
Stereotypically us Brits are supposed to be always polite and amicable, believe me that's not the case. However if we require special arrangements for our health conditions we seem far more accepting of providing 'evidence' to get that. I realise that in America there's a big thing about not having to state your disability/health condition but it's not as painful to do it as some seem to think. In a perfect world, I and others would be perfectly healthy, unfortunately we don't live in a perfect world. Whilst it's not what I would call fun telling people that I suffer from Dystonia, it's just part of my life that sometimes I have to.
Having surgery 2 years ago where probes were implanted in my brain, I can no longer go through metal detectors. I've been issued a card that international airports are expected to recognise and yet when we visited Disneyland Paris last year I was advised that I needed a doctor's letter dated not more than 2 months previously to get through Disneyland security despite having a card that's recognised by international airports and that I'd also have to be physically searched. So I had to ask my neurologist to write a letter which he did to visit Disneyland.
The funny thing was that when we got to Disneyland security they just sent me through the CM entrance which is at the side of the security checkpoint. Not only did they wave away my letter that I'd had to obtain but they barely looked at my card the airports checked. Also there was no search of me whatsoever, no pat down, no questions and no emptying pockets or anything else. This happened on all 3 visits with different security people every time.
I also am often asked by the airlines to provide proof of my Dystonia when requesting an aisle seat to allow my arm to be able to stretch out into the aisle to avoid as much cramping as I would otherwise get during a 9-10 hour flight. Again this doesn't really bother me as it just seems like the simple thing to do to get what helps me.
I'm rambling off topic her and apologies for doing so. My point is it always strikes me as a completely different viewpoint from you wonderful American people I visit every year when I read people on here getting so passionate about not having to tell others what your disability is when requesting things needed because of it. It's not a criticism, just an observation.