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If as I understand it the rest period was to be 10 hours between duties, it could without doubt be fatiguing. I reckon realistically you'd be lucky to get six hours 'asleep', most of that restless.
Do you honestly believe if minimum rest was reduced to ten hours, it would rarely be used? Reduced rests (ie requiring Commanders discretion ) are very rare in my experience and night splits, although legal, are definitely tiring.
Call it fatigue / tiredness, whatever the hell you like, I know how knackered I often feel, within CAP 371 limits.