I suspect my dad prevented this glitch from forming in my young mind. When I was a child, one of his favorite ways to tease me was to stand over me, and demand that I float in the air. He'd raise his hands over my head and pull them up, all the while saying "float! float in the air!" Of course I'd laugh, and I knew it was impossible, but I'd still try I'd strain, and rise up on my toes, and jump up and down, but I couldn't do it. Then he'd shake his head, and admonish that I'd better learn soon, because it would be too difficult to learn when I was "old and fat" like him.
The part of my brain that knew it was impossible would laugh, but a part of my brain would still try with all it's might to float, and quickly learned that it's impossible. Flying dreams are pretty difficult for me, now. I still find myself straining the way I did when my Dad commanded me to float.
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.