What Causes Tightness In Throat After Taking Sulfameth?

I have had a sore throat since yesterday. I took some of my husband's leftover sulfameth, which I have taken before. One this morning and one around dinnertime. I just went to bed around 11:00 and my throat feels like it is tightening. I am afraid to go to sleep. I don't have any hives or anything else wierd.