I doubt the shift actually came out of the blue. Something bad must have happened to you.
Maybe you've always had issues with it but are unable to scrape by anymore due to increasing expectations? I've always had stress issues but eventually it became too much and I caved inwards
Probably around 3rd year of highschool. I had always been pretty lonley and quiet but I always thought I would find some friends and a gf eventually but by junior year it had fully set in that I would most likely be alone forever, sure I have a couple good friends but they're just as hopeless as I am and I doubt itll last forever, every year it seems we talk less and less, my online friends grow distant as well. Other than my family, which I can hardly relate to at all, It's just a matter of time until I will be truely alone.