Why does it seem sometimes like mixing different alcohols in a night makes one sicker?

I have a friend, for example, who gets considerably sick when he mixes beer and shots of rum in a night. I often can't drink Long Islands, I suspect because of all the different types of liquor and the sugar content. I tend to get sicker when I drink both vodka and whiskey in a night. Is there a reason one might get sicker from mixing liquors/types of alcohol? Why?

This is the best explanation I've heard. It is often said "beer and then liquor, never been sicker. But liquor and then beer, and your in the clear." If its safe to mix them one way, but not the other, then obviously there is nothing wrong with mixing them. If you start with beer, you get buzzed or drunk BEFORE you start on the harder stuff. This means you start to lose your "good judgment" before switching to stuff that easier to OD on. If however you start with the strong stuff, then switch to beer, you are switching to something that is weaker. This means you will have a harder time drinking enough beer to make you sick. This might explain what happens to your friend who "who gets considerably sick when he mixes beer and shots of rum in a night."

As for you, I'm not so sure. Perhaps you are getting drunk faster when drinking these drinks so you end up drinking to much. You also don't say what you mean by "sicker", so I don't know if you mean sick as in vomiting, or sick as in monster hangover the next day. (hangovers are not caused by sugar drinks, but by dehydration from the alcohol. Drinking water while drinking alcohol should prevent most of the hangover. I still haven't figured out how to stop the whiskey $hits...)

Mixing isn't the problem, it depends what you drink. Wine goes down smooth, but has a alcohol content of 13.5%, and 2 or 3 glasses is like drink 5 or 6 beers. But you don't feel as full, so you can drink more. Hard alcohal, you can shoot straight and the content is 40% a ounce. When you tie all three together you are in trouble because they all taste so different, your pallent is cleansed and it's like starting over all over again.