Common symptoms of a hangover like headaches, nausea, and anxiety are caused by chemical changes in your body and brain that accompany drinking. Alcohol suppresses a hormone called vasopressin, which normally prevents you from urinating too much. Without it, you pee more and become dehydrated (cue morning headache). Other chemicals called proinflammatory cytokines are to blame for your flu-like symptoms, while changes in brain chemistry — not your choices last night — are responsible for so-called "hangxiety." Hangovers and the horrible headaches that come with them are caused by chemical changes in your body that take effect as soon you down your first drink. Following is a transcript of the video. Ahhh.