I believe it, I personally experienced something like a psychotic episode while on a meditation retreat. Also a panic attack, a few hours before that. No prior history of panic attacks or psychosis.

I actually think that some of the benefits of meditation are adjacent to psychosis, in a way: as you get closer to the "insight" that is the intended result of Buddhist meditation, you are also flirting with losing your grip on reality.

In my case, it went fine. I resolved the experience and integrated it. But I could see how it might go the other way for some.

Professor Britton at Brown has made a career of studying these kinds of experiences, plenty of examples here:

https://www.brown.edu/research/labs/britton/research/varieti...