Oh god I get this when I can't sleep really late at night and have been playing Halo or Cod or other repetitive multiplayer games (no flaming intended).
The other night it was 4am and I had watched "The Thing" and all I could fucking think about was a million different situations where I was in that movie, so I was suspicious about everyone, logically trying to determine who was infected, trying to think how best to isolate and infect everyone and desperately trying to defend myself ALL. AT. THE. SAME. TIME.
It was hell. So glad when that night finished.