In my search for methods to increase the activity of 5 α reductase, I came across the following little tidbit: alcohol intoxication increases allopregnanolone (this has "common knowledge" status and is referred to in a number of places, but that was the only real study I could find quickly).
There are a number of threads describing cognitive benefits of hangovers, but none of them propose this mechanism. However, allopregnanolone has potent neuroprotective and neuroregenerative effects, and IMO makes a more plausible mechanism for explaining these magical hangovers than GABA agonism and other hypotheses thrown about.
Anyway, there are a lot of ardent teetotalers around here, ranting about how dangerously neurotoxic booze is, so I thought I'd throw a metaphorical drink in their faces. Na zdrowie.