I think it’s probably fairly common. And it’s not that - of course it’s important to distinguish between all the things that are lumped together under ‘chronic illness,’ since they’re very different and we experience our disabilities differently (I experience my different ones differently!).
However, the way certain illnesses are dismissed does a lot to produce that kind of anxiety - and particularly invisible, or even kind of sort of potentially invisible ones (hence getting it over asthma as well as autism and depression!). It’s like - if you can seem remotely normal, firstly, you should, and secondly, you are. Ugh.