My mother has that problem when people wear a musk based perfume. It constricts my mother's throat.
I get something similar. I can drink orange juice, or grapefruit juice (thought I don't particularly like grapefruit juice), and I can drink vodka, BUT, I can't mix the orange or grapefrut juices with vodka. As soon as I do that, one drink and my throat feels like it swells inside to where its difficult to swallow.
A constriction in the throat is serious, in my opinion. I'm guessing, just because it's common, that you might have a citrus fruit allergy. The oils from the juice probably dissolve in the alcohol, which makes them more easily absorbed through the mucous membranes of the throat--so you have a more severe reaction than if you just drank the juice plain.
This is just my guess.