1. My understanding is that these videos often talk about very general symptoms, that could be caused by these mental disorders -- but also by a lot of other things.
2. The videos take on an authoritative tone, which does a good job of convincing people (especially kids). I've written about this phenomenon (albeit playing out in written form) on HN before:
> Welcome to the internet ¯\_(ツ)_/¯
> It's not hard to find highly opinionated people making assumptions while confidently believing they're right. If you look closely, you'll notice this all the time on HN and Reddit and basically anywhere that allows people to comment.
> The scary thing is that many readers will also often take anything said confidently enough to be fact. This is also basically how a lot of disinformation works. Say it authoritatively, and you'll become an authority on the matter to many people.
3. The 'nocebo' effect is very real! It's the opposite of a placebo effect, where if you believe you have an illness, your body actually starts showing symptoms.
4. I'd believe that in a lot of cases it's less about a kid consciously thinking "Ooh it's trendy to have this, let me say I do", and more like kids thinking "Oh this seems to be a widespread thing, and I experience these symptoms sometime (I space out! And I have trouble sleeping! And I have a jittery leg! and so on), sure seems like I might have this!"
5. Very important quote from article:
> "If you spend 15 minutes, 30 minutes, 60 minutes viewing people talk about these disorders over and over again, that can make it seem like these conditions are a lot more prevalent than they actually are in the world,"
Repetition makes it seem like a bigger deal, and makes it stick around in the kids' head. So the next time they space out in the classroom naturally the thought might occur ("Do I have dissociative disorder?").
6. If lots of kids start showing up to doctors' saying they have (for eg) BPD when they don't, it'll be a lot harder for those with actual symptoms to convince doctors of their situation and receive proper medical care, which is very worrying.
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All this said:
1. I'm just a user of the internet - not a psychologist, nor someone with relevant formal training, so please take my hypotheses as just that -- hypotheses, not fact.
2. I haven't actually watched many of these videos, so if someone has links, please share them! I think a lot of people on HN might like to watch them and analyse what's going on.