Two things come to miond. First, I was at my sisters house on winter and decided to take a walk. They lived in a wooded area - 1/4 mile driveway to a 2 mile private road all surrounded by trees. I get about half way down the private drive and I pause to look up at the stars. In that instant my mind suddenly presented me with extremely vivid images of all the nasty monster-things lurking in the woods waiting to jump out and kill me. I froze in place - terrified. I stood there for over 10 minutes before I worked up the courage to move. Then I RAN back to their house.
The mind is a terrible thing when it decides to fuck you over!
Second one was being in an elevator when it decided to go insane. I got in on 1 and pushed 8. It got to about 3, then dropped back down to 2, rose up to 4, dropped down to 3 and so on. I was FRANTICALLY pushing buttons but nothing worked, not even the stop button. When it finally stopped at a floor and opened the doors I flung myself out and dropped to the floor sobbing. I have reoccuring nightmares about elevators now and I get jumpy if I'm in one and it does ANYTHING odd.