'round 1850.
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(yeah, taking photos with your mobility aids isn't new either)
It comes and goes throughout history, but social media has definitely spread the trend far beyond what ever existed before. It's a social contagion. They see all the attention and praise and sympathy someone else is getting for being sick, that they don't have to work/go to school/grow up because they're too fragile and delicate, that no one bullies them, that they have instant oppression olympics points ("I'm disabled!"), and they want it too.
But people were reporting illness scammers in forums from the late 1990s, people who told radically unbelievable stories like having a stroke mid-chat and created sockpuppets claiming to be family members to validate the claims, bored housewives making up dying teenagers... Insta and youtube just put a cute, disney princess face to it.