(Don't take this story seriously. And remember that hangovers may often be migraines.)
The story is told, though I don't remember by which, of Hilaire Belloc and G K Chesterton taking a walking holiday in the Highlands of Scotland.
At the end of the first day, exhausted from their physical exercise, they retired to the bar and decided to engage in a scientific experiment. They ordered a whiskey each, mixed with an exactly equal amount of spring water and no ice. They went on to enjoy several such drinks that evening, and the next morning they woke up with hangovers.
On the second evening they repeated the experiment, but using Irish whiskey instead. Again they mixed it 50-50 with spring water. They had several drinks, and woke up the next morning with hangovers.
On the third night they drank a single malt Scotch with spring water, and woke up the next morning with hangovers.
So they came to the conclusion that there must be something in the water.