I will try to avoid giving medical advice, I think this can be classified as information. Alcohol does a number on our livers and our brains. If we are chronic daily drinkers, as I was, our livers adjust to that by using alcohol to create energy. That is why alcoholics often suffer from malnutrition while they are active: alcohol literally takes the place of food.
I recall getting that surge of energy after my first drink(s) of the day - I avoided breakfast and often lunch. But, I had energy from alcohol.
The brain also goes through some major changes on a constant diet of alcohol: the brain compensates for the constant feed of a major depressant of the central nervous system, (alcohol) by creating it's own endorphins and similar substances that keep us "up".
Your liver and brain can go through a long period of readjusting after being deprived of alcohol, and that can certainly affect your energy levels, especially since alcohol was such an energy provider.