Another factor is that our jobs are often highly "scripted" or regimented, which allows us to "function" despite sleep deprivation. If you found yourself needing to do complex formulas or compared reaction and actual choices to what you did when you were not sleep deprived you might not feel the same way. I find myself seeing ghosts and second guessing my actions after being awake for 48hours or longer.
Reed
P.S. I agree whole heartedly with Carl