Testing for fatigue is difficult. It can be done with stress tests in
which you would ask the subject hard questions on a sheet of paper and see
how well they answer them. The problem is you would also need a constant or
a test done when the person wasn't fatigued, in order to make a comparison.
Without that, the poor person may just not be very bright no matter how awake
I will ask around and see if anyone has something similar to a
"breathalizer" for fatigue.