When I'm sleepy enough, I usually think that my brain has Internet access.
A few months back, I was half asleep and thinking about a certain person. For a moment I wondered whether the NSA now knew who I was thinking about, since thinking about someone obviously requires going online and retrieving the concept of that person from a central server.
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.