When you've gotten so hammered, smashed, or whatever you prefer to call it that you can't lie whether you want to or not or are actually aware of whether you can't lie or not.
Alex: Why am I under arrest officer?
Cop: SIr, you came into the precinct last night seriously inebriated and when we asked what you did before coming here..... you confessed to murder, and told us where to find the body.
Alex: Damn it..... I must have been truth drunk!