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.
I have a similar dream frequently, in which I levitate simply by pointing my toes upward, causing me to rise a few feet off the ground. Alternatively, I sometimes fly horizontally like Superman. This has led to the repeated experience of waking up and realizing I can't fly after all, and subsequently dreaming it and realizing "I can fly after all." But there are also times when, after starting to fly in a dream, I recall that this is something I can only do in dreams, and thereby infer that I'm dreaming. Sometimes this induces a creepy paradox feeling that compels me to wake myself up; at other times I'm comfortable continuing in the dream even while knowing it isn't real.
There are also times when I'm in a state close to sleep -- either having just awakened, or having become drowsy later in the day -- when my brain is in a state that makes me feel I should be able to fly. At these times I can't resist trying to "will it," even though I know intellectually that it's impossible.