I am one of those people who never got hangovers, and I used to put down a lot of alcohol. Even after binging on alcohol for 3-4 days, I would come out of a bender feeling physically fine. I used to think that it was some great attribute, but now I realize it was more of a curse so to speak. When other people would be sleeping all day and feeling like crap, vowing never to drink again, I would be waking up early, feeling fine, and planning by next session of debauchery.
I think it's one of the things that prevented me from curbing my drinking when I went on a bender, because I would wake up feeling fine, except I had to piece together all the destruction I caused in the process.
I don't know what caused me never to get hangovers other than I am in pretty good shape, but I don't know if that has anything to do with it. I know people who get hangovers only after a few drinks, I also know people who black out after a few drinks, I think it's all genetic.