I'm trying to remember my neurophysiology and neuropharmcology from nearly 50 years ago.
Alcohol is a neural depressant and reduces, for instance, social inhibition. It reduces the efficiency of motor activity and slows down reaction time. In commercial aircraft cabin air pressure is at a rather lower level than on the ground - lower air pressure increases the rate at which alcohol is absorbed into the bloodstream thus the neural depression effect may be more rapid than at ground level.
If anyone thinks that the effects of alcohol are unimportant in a commercial aircraft cabin, they should consider the reported incidents (I think I have seen two recently) where some enterprising travellers tried to open emergency exits in mid flight.
