I am absolutely convinced that alcohol (not the day of) has something to do with speech impairment. I tend to drink a lot on weekends and the withdrawal effects on the bodies central nervous system I know for certain messes me up. When I have to speak I try not to have any alcohol or really very little for up to a week in advance. For me the difference is dramatic. I read the submission on caffeine and I think alcohol abstinence is crucial too.