Why do certain food textures make me gag?

I was eating a turkey sandwich (made from leftovers) and there was a chunk of turkey fat in my sandwich, and I gagged a couple of times (but didn't vomit). This happens to me with fats on meat, they're squishy and chewy and very hard for me to swallow without wanting to gag, I usually cut them off or spit them out. My dad thinks it's weird but I can't help it! What causes this and why does it only seem to happen to me?