you skin, more than your bowels, is the dumping ground for all you've consumed in the last 48 hours and harder to flush than your colon. The next organ is your lungs, absorbing VOC's (volatile organic compounds) in the oxygenation exchange in your lungs, and expelling them into each exhale:
That is why you could swill mouthwash for hours...to no avail!
Fatigue IS the silent killer though* and while we may have a great social experience with alcohol and it's effects, I am not sure we have enough knowledge (properly shared) about the relationship on rest deprivation with judgment, perception and responsiveness, especially when the stresses of high altitude are factored in.
In reality, you are never OFF duty, and since recovery time takes several hours.
I had an extensive chat once with someone... I tossed out the idea for a pre-flight cognizance check software I was thinking of developing. Basically a laptop that basically tested the pilot with some scenarios and questions and math prior to taking the plane, a five minute electronic version of the "Horizontal Gaze Nystagmus Test" this test would be easy to perform when alert and well rested, but very hard if not. Borderline cases would have to be approved before the pilot could continue. The feedback I got was that airlines would rather not know!
*caveat: because we can smell drunk but we cant smell tired