I noticed that as my alcoholism progressed to the rather severe stages my hangovers became less and less predictable. One night I could drink 40 beers and wake up feeling fine, another night I could have 4 and wake up with the worst hangover ever.
I'm sure that getting older had something to do with it. I'm only 35, but my body is still not that of a 17 year olds any more (even though I forget that and treat it that way sometimes
). I also think, and this is just my own little theory, that once we reach a certain point in our drinking our bodies just get tired and we go through times when we just can't metabolize and eliminate all the toxins that we pour in.