There's a word for something, that when remembered--or a person that when spoken to--brings you back to reality and the knowledge that you're not insane. I keep wanting to say "touchstone", but I don't think that's it. "Cornerstone" kind of works (and is probably why "touchstone" comes to mind), but is more about a foundation you build yourself upon, rather than something you come back to.
I think I'm looking for a synonym for reality check. It's also the opposite of something that gaslights you.