I think that you may be jittery/distracted because you NEED a drink, the way smokers need a cigarette and once you've had your hit you feel more relaxed.
My 2c
Not at all. During work hours I'm pretty focused and don't do any talking or surfing. Plus I've never even drank coffee so I don't think it can be the jitters.
I don't think so, well not conciously anyway. I don't drink often. Perhaps I'll get a bottle of gin once ever 2-3 months. I've just noticed my personal projects would get a boost during the wet season.