I believe that also your internal chemistry is out of whack and needs to rejigger itself back to the normal equilibrium edit: according to this page[1] there's

I believe that also your internal chemistry is out of whack and needs to rejigger itself back to the normal equilibrium edit: according to this page[1] there's a combination of things: - an inflammatory response - irritated stomach lining - blood sugar crash - blood vessels expand - alcohol can prevent deeper stages of sleep so you aren't rested the next day [1] https://www.mayoclinic.org/diseases-conditions/hangovers/symptoms-causes/syc-20373012 https://www.mayoclinic.org/diseases-conditions/hangovers/sym...