Flying when dead is incontrovertibly a bad thing, hangover or not
The world is a poorer place as sub-editors bite the dust.
I do not fly with noticeable headcold or other acute symptoms but I don't buy the line that everyone has to be happy and totally healthy all the time to get through life, including life in aviation. Presumably most people recognize this view is a fantasy promoted by lifestyle TV programs and newspaper magazines (and phamaceutical and complementary medicine companies).
I don't want to go back to the situation where e.g a CFI could start the day with a strong coffee, a handful of BP pills and a ciggie or two, but I'm not about to get too precious when a recovering pilot makes an informed decision to fly. As others have noted, elements of that decison could involve the nature of the medical condition, class of operation, number of crew, prevailing weather, length of flight, etc. If you're a typical human, with more than a few years on the clock, you are going to have to get used to making these calls if you want to get off the ground. It doesn't hurt to do some thought experiments ahead of being faced with real situations - helps maintain some objectivity, in my experience.