The sad thing is I only know this from following some radfems on tumblr, I have avoided as best I could the more extreme parts of tumblr but occasionally the weirdness spills over (like I found out about people getting tics from tiktok and stuff like shifting and otherkins) from people reblogging stuff. Mostly I follow aesthetic and lifestyle tumblrs. I'm not looking for the weirdness, it just appears.

surreptitiously Googles 'shifting' and 'otherkins'<

The DID stuff with people taking having multiple personalities used to be otherkin, thinking you had the soul of a being (usually fictional) in you so you actually ARE that character. It was all crazy fandom roleplaying, but they found a medical label they can appropriate to sound "real"