The FOM uses the word fatigue, but does not define it. From NIH, "Fatigue is different from drowsiness. In general, drowsiness is feeling the need to sleep, while fatigue is a lack of energy and motivation. Drowsiness and apathy (a feeling of indifference or not caring about what happens) can be symptoms of fatigue." So basically if you are tired fine, but if you are so tired you don't give a sh*t, watch out. The problem is when you don't give a sh*t what motivates you to call in. - I have only felt this way once. Why not give a pilot the greatest opportunity to sleep as much as possible before he flies. To the poster that does not understand the stanby delema - set your alarm about 4 hours prior to your next am show. Then drive to work and get a room for a few hours then go to work. Do that and then PM me.