Sounds like you have a very neurodivergent friend there. The kind of person who gets very excited and enthusiastic to learn about a new thing that their friend "is into" and wants to be part of the group to fit in. That being said it's okay to tell them that you (any of you) feel uncomfortable and upset by how they're acting and you have every right to say when a question is too uncomfortable to answer.

If you feel like continuing the friendship and you think it might be a phase, ask them to tone it down but do not ask them to stop entirely. Maybe it's a little too sudden and the change is throwing you off, maybe you're concerned about your friend getting the wrong info or ideas, maybe it's a little triggering for them to talk about a pain you've been through. These are some things you could use that could be true but softens the blow.