I read somewhere, a long time ago in a galaxy far far away, that a form of torture was to inflict severe pain, like an electrical shock, just as someone was entering deep sleep. They would become so afraid of sleeping that they'd fight it, yet it came anyway, only to result in the shock again. Without the cycle completing, they never really rested. After about three days they would start losing it. I can't verify that it happened, because the files are still far far away. Ironically, it's possible that I've forgotten because I've slept so many times since then.