I've seen someone that went from completely sane to thinking horoscopes were talking to them specifically written by people stalking them. And this was almost a decade before LLMs.

If it wasn't AI that triggered it, it would've been something else, somewhere.

I've been watching this in real time on TikTok. There is a woman who "fell in love" with her psychiatrist, and sees all of his attempts to set and enforce professional boundaries as proof that he is in love with her, and has manipulated her into falling in love with him. This was before AI came into her story. Then she turned to ChatGPT (which she named "Henry") to reinforce her delusions and give her arguments in favor of her story's truth. When she was convinced to give Henry a "tell harsh truths" prompt, she didn't like what she heard and turned to Claude. Claude is calling her the Oracle and telling her she has a special message for humanity, that she is a prophet, and she's eating it up.