Alcohol causes headache as a result of its effects on
blood sugar. If you already have hypoglycemia, an
alcohol-related drop in blood sugar may bring on head pain. Some alcoholic beverages contain tyramine, histamines, and impurities introduced during the fermentation process, which can also cause a painful headache. Drinking alcohol also causes you to urinate a lot, which can dehydrate your brain cells and cause headaches.
It will go away on its own.
Refer http://www.headachenech.