When I first put out a call for ideas on this topic, I was rather surprised at not only the number of responses I received but as often who it was replying. That’s on me, that surprise, and, knowing what I do, I shouldn’t have been.
The reason there’s so much stigma surrounding most mental health issues is that people who’ve never dealt with it themselves cannot understand it like they could a heart attack, or the loss of a limb, even though they may never have personally experienced those, either.
There is a false assumption that someone suffering this, or again any mental health issue, will show it on their face like a rash (that spells “nutbar” across their forehead, maybe?) or in their general, casually observed behaviour.