I don't think social class matters at all.
I grew up upper middle class, my mother worked in medicine and my father is an international engineer. My mother was bipolar, it did not end well. She had the money for all the expensive doctors and name brand medication which I think made it worse. She was always learning about something new which were basically medical fads and would try them. Plus my parents were always about image, because it would affect their careers, so no one really knew my mother was bipolar and a lot of her hospital stays weren't beneficial because she got different treatment. Like she wouldn't have to stay or her symptoms were played down. My father also to this day denies mental illness exists.
My ex husband's family was low class blue collar, although he never worked. They were able to take advantage of a lot of programs that were made available to them, and never really seemed all that stressed out. They didn't really have high stress careers and would work 40 hours or less a week. And if needed, it wasn't a big deal to them to quit their jobs to take time off when there were stressful things going on. They didn't have money, and there was always an option for them via social services and unemployment insurance.
I was for maybe 5 or 6 years very poor. Like no car, walking everywhere, worrying about food and bills all the time. But I wasn't nearly as stressed as I am now being upper middle class earning 6 figures a year and I had down time because I only worked 40 hours a week or less. My PTSD developed during the time that I've had money. I've worked in a high stress tech field for the past 10 years. I don't have the option for failure or else I could lose everything. I do not make my PTSD publicly known and have to keep symptoms hidden from coworkers. I panic about having panic attacks at work. There's a lot more pressure on me and I do not have down time at all, even for medical issues. I had surgery on my throat once, took the morning off for the surgery, but as soon as I was back home, I was working from home.
Sure, I could downgrade my life. But I have a teenager going to college and I have a mortgage, and car loans. I think it would be tougher for me to change my current lifestyle.