Spoilers for Stranger Things and Hannibal follow; trigger warnings for gaslighting, medical abuse, and narratively satisfying vivisection.
"I'm not crazy!"
It's a line you hear a lot in everything from urban fantasy to horror to paranoid conspiracy thrillers. The idea is to communicate that what's happening is real, and not just a delusion.
As far as throwaway utilitarian lines go, it's fine enough I suppose, but I think we can come up with a better line. Stranger Things, a Netflix original series which is so aggressively 80s that I keep expecting while watching to spontaneously be enveloped in black leather and chrome, might give us a bit of a glimpse of what a better line might be:
"I'm crazy, but I'm not wrong about this."
The basic narrative of Stranger Things follows a group of kids and adults battling against a Sinister Government Conspiracy and the Horrifying Extradimensional Monster that the government creeps have unleashed. And also there's a girl who can flip vans USING MIND BULLETS.
THAT'S TELEKINESIS KYLE.
What's really notable in the series is that major protagonists are, in fact, crazy, in the sense that they struggle with a variety of mental illnesses and traumas predating the start of the story proper. But that doesn't make them wrong. You can be both mentally ill in this show, and a main character, and correct about government forces fucking up your life. This is important to me as someone mentally ill in an exciting variety of ways, and as someone familiar with gaslighting and people taking advantage of my own uncertainty about my perceptions. This show, in setting out a narrative where people are explicitly suffering from various conditions, and who have to fight against those trying to take advantage of them because of this, is doing something important culturally.
A real good starting point for analyzing this is one of the show's absolute best characters: Joyce "Wallfucker" Byers.