It happens. The weirdest I ever had was when I was fitting more memory in a PC. Move it all into the middle of the room. Checked everything working ok and sat beside it. Took it to bits, fitted memory, put it back together ... No keyboard. It was there before, I hadn't moved , it must be here ... No, no sign. After five minutes I got up, looked around once more, then went to the study where it was before and picked up a spare keyboard. Went back ... And there was the original, exactly where it should be.