Why do I throw up when taking shots?

I have some bottles of hard liquor; bourbon, whiskey, spiced rum. I love how they all taste, but I struggle with shots. I usually gag or throw up, but sipping I can do just fine.

This happens on my first drink of alcohol for the night.

Obviously I am just going to sip from now on, but why do I gag or throw up from shots of hard liquor?

Like I said…. I like the taste… So it’s not that.