I remember seeing Jack Elliot so drunk that he did the same set twice. I was annoyed that he did not have enough respect for his audience to exercise some self control. Another time Ian Tyson became belligerent to the audience for no reason that I could discern.

However, I also find that performing music at its best (to me, at least) is an "ecstatic" experience, not a "thinking" one, kind of "in the zone".

It seems that many performers drug and drink to get to that state. Unfortunately, drugging and drinking is an inexact science and "taking the edge off" may leave you unable to tune or to communicate with band members or the audience. And it is compounded when more than one indvidual is under the influence. If you are in doubt, tape your performance, tape recorders don't lie.