that kinda happened to me last night in bed. I was just lying there and scenes from a horror movie I had watched a few months earlier started playing in my head. I said to my brain: shut up, but it didn't stop. I then buried myself under the covers and started sucking my thumb in fear. (jk on the last part)
When I was 5 or 6 I watched the first Jurassic Park movie, and the first scene with the velociraptor scared my tiny ass so much that I would sprint by any closets and bathrooms for the next few days