Favorite losing touch with reality movie?

I'm in the mood to watch something that actually scares me. The older I get, the more the idea of losing my mind scares me. Losing touch with reality, things get more and more confusing/disorienting and you don't know if what you're seeing/experiencing is in your head or if it's real life.

First one that pops into my mind is the Lighthouse.

Any other favorites?!