Because the microwave on my floor was busy some weeks back, I walked up to the next floor to use their (identically located) microwave. I met there a colleague, who thought I had come to his floor to see him because of some work-related problem. He said "Oh, I thought you came down here to [etc etc etc]".
As a result, the bit in my head telling me how to get back to my own floor was flipped, and I walked up (further) to the next floor. Only when I got to "my" cube (since all the floors are essentially alike) did I realize what had happened.
"Turning the world on its head with a single word! Eloquent guy!" --Terje Bless