For me it was trauma . I think it’s a set of factors
I think there are many factors. But no I don’t think it had its Genesis in any aspect of modern living. It has likely been around for millennia. We just discovered it well enough to pin it down and classify it fairly recently (like most mental disorders.)
Any origin of mental illness comes from a mixture of genetics and environmental triggers (called the Gene-Environment interaction). If you have the right genetic predispositions for mental Illness, a traumatic event may trigger those predispositions. Another thing too is to think about Maslow’s Heirarchy of needs. In developed countries like the USA, we are lucky to not have to focus entirely on food and shelter needs (usually). We have basic needs met, which then allows us to grow our personalities, knowledge, and become our true selves (he calls this self-actualization). This is why mental illness has been such a big deal in this century compared to others- we actually have time to think about mental problems and not trying to hunt a chicken for dinner lol. Just my two cents.
My best guess is that it’s leftover from our cave man days when there were more legitimate and intense threats. I like to think of it as the oldest part of my brain chiming in where it’s not so needed. Doing it’s best to keep me safe, just waaaay misguided about what that means these days. 😄
There’s some evidence it has to do with inflammation, like in the case of PAN/PANDAS.