My sympathies. I never spent any time on 4chan. But between doing some desktop publishing and helping friends with abuse on the first web-based chat, I saw a bunch of things I could not unsee. It took me maybe 15 years for that stuff to not come back as what they call "involuntary autobiographical memories". It has now faded to the point that I can't bring the full images back at all, just hazy, untraumatizing vague versions. I hope you get there soon!