Headache, nausea, etc. following a drinking carousal. Colloqual.--Mitford Mathews's A Dictionary of Americanisms, 1956
Figuratively, an unpleasant aftermath or reaction; depression, "blues", clamour, uproar.--Sir James Murray's New English Dictionary, 1928
Feast Day of St. Armel, a patron of headache sufferers. Gervase Markham's The English Housewife (1616) advised: "For headache you shall take of rose-water, of the juice of chamomile, of woman's milk, and of strong wine vinegar, of each two spoonful; mix them together well upon a chafing-dish of coals, then take a piece of dry rose-cake and steep it therein, and as soon as it hath drunk dup the liquor and is thoroughly hot, take a couple of sound nutmegs grated to power, and strew them upon the rose-cake. Then, breaking it into two parts, bind it on each side upon the temples of the head, and so let the party lie down to rest, and the pain will, in a short space, be taken from him."
Well, I can certainly see how that might -- HUH???