There are many reasons why a person could be passing out. A self brought on reason would be having to much alcohol. Some people also pass out when they find out good or exciting news, or if something grosses them out. Some medical reasons could be low blood sugar or low blood pressure, and these are just two examples of the many medial issues that could make you pass out. If you are passing out you may want to contact a physician to make sure you are not having some health problem. If it is self induced by drinking to much, maybe try drinking less.