Vodka gives me really bad reaction?

So yesterday my friends and I had a party at home where we make our own cocktails. We wanted to be moderate so we calculated alcohol amounts in each drink (same volume)so that the drinks we make is 9% alcohol v/v. I made my cocktail with vodka. One hour later I vomited 7 times and had to lie down because it was just unbearably painful.

I made my cocktail with other hard stuff like whiskey but never had this horrible reaction. However, I do recall getting sick from half shot of vodka years ago. I don’t think it’s the alcohol but something else in vodka that really mess me up. Any ideas?