Hello It happens when you are not taking much water along with alcohol as alcohol makes you dehydrated. You need to drink lots of water to maintain the blood pressure and circulation to your brain. When you drink alocohol your blood pressure goes down and oxygenated blood doesnt reach your brain fast enough causing dizzyness and sweating. Sweating increases the dehydration resulting in increase of the cause. Take loads of water with alcohol and avoid to much alcohol as hypotension can sometimes result in loosing consiousness and you could hit your head somewhere when falling suddenly. Thank you