It's generally when you're stuck in a loop of reading negative posts/articles. I think the phenomenon comes from how when you read a negative article/piece of news you feel down, so you want to scroll further in the hopes of seeing something positive to lift your spirits. But then of course it's only more negativity, and so you keep going. And the algorithms of Twitter/Facebook knows this, so they don't tend to help you find something positive.

I think alot of it relates to just scrolling through news and wanting more content/headlines. It's not that users are necessarily seeking out bad news or "doom", it's just that, given the state of the world today , that's what a lot of the news ends up being. I think I often engage in "doomscrolling", but I'm not doing it because I want to see bad news, I'm an information addict and I'm just trying to get as much content as I can. Reddit fed that habit well, but I've moved on from there. And it's not necessarily a bad thing if Lemmy can't feed that addiction, not seeing new content pushes me off and forces me back into the real world or on to other sites/apps. I'm fine with that, I hated my constant need to flip through Reddit whenever I was bored before.

It's been a thing for a while, basically just mindlessly scrolling for hours on end on a neverending feed

I prefer Doom Metal.

Covid era when many people had nothing to do, were more worried and anxious than usual, and the internet seemed full of concerning and bad news. The term has never meant that much to me personally. I’ve only regular scrolled.