The progressive nature can come from the body adapting to dealing with it, the body adjusts to dealing with all poisons, the more it has to deal with the better it gets at it, so for the alcoholic they need to drink more and more alcohol to get the same buzz as before, the body becomes more efficient at dealing with it . . . however there is a ceiling, there is a point at which alcoholics no longer have hangovers, hangovers are created by the body creating a substance as it breaks down the alcohol, once the liver ceases to be able to break down alcohol, no hangover takes place, the alcoholic is in real trouble at this point, as liver function is seriously impaired!!
From my own story, I started having 2 pints on a night out, that was my fill and I then went home buzzed and went to sleep, fast forward 5 years I was drinking a half bottle of whiskey a night, a full bottle on weekend nights, now I never lost a job, lost my driving licence, no relationship issues, no financial issues, but it was only a matter of time!!
A full bottle of liquor a night and then going into work the next day, that is gonna cause problems eventually no matter how "functioning" you are, something had to give, thankfully I made the change to Sobriety, but the future was bleak had I continued on that path!!