To me, a hangover is the start of my withdrawal. When I drink, my body stops producing dopamine, because the alcohol binds with the dopamine receptors, then the next day when the alcohol is gone my brain and body freak out because there's nothing to bind with those receptors anymore.
Even after a period of sobriety, if I have just one drink, my body remembers that when I take in alcohol it doesn't have to produce dopamine anymore, so it shuts down production.
That's how kindling works on me, and why, physiologically, for me at least, just one drink gives me the same withdrawal as the my worst bender. A hangover was just the start of my withdrawal.