So I trudged my way down to the refreshments area and made myself a cup o' joe. With some chocolate in it.
Almost instantaneously, I was revived.
Which leads me to think that it must be more psycho-somatic than anything else. There's no way the caffeine would have had time to reach my blood stream before I was feeling more awake.
Apparently, I get revived simply thinking about the cup of coffee in my hand.
What wakes you up?