Once when I was maybe 13, I played a card-guessing game with my father. He would hold up a card and I would guess what it was, then he would show me what it was. For what seemed a very long streak -- like 15-20 cards in a row -- each of my guesses was not the card my father was holding, but the next card he held up, drawing from the top of a face-down deck. Although at the time I was inclined to believe in ESP, I knew this was anecdotal evidence, however bizarrely improbable a coincidence it might seem. In retrospect I wonder why we never repeated the game or tried to specify a hypothesis to test.
A few years ago my brother told me our father was an amateur hypnotist, and that he has memories of being hypnotized by him without his informed consent. I now wonder if he did something similar in this instance -- for instance, using a suggestion to prevent me from noticing that after each guess, he was searching through the deck for the right card to hold up next time.
This is a kind of "X files" thread.
Post experiences which spooked you, which made you doubt reality, mathematical or physical laws, your sanity, memory or perception. The more improbable the better, but no second-hand legends please, share only what you personally experienced. If you had the event later explained rationally please use rot13 to avoid spoilers.