Then you're stuck with either
A: hit it with a cough to try and get it out, but now you're either going to spit it out leaving a dissolving mess you're stuck to try and take again / it just lands dead center of tongue/roof of mouth
B: Hope your water is both nearby and actually full and don't choke

Gotta love the ones that instantly melt and taste just like ... Soap with a hint of burnt plastic. In addition, they always stick to your tongue. So now you gotta hope you get it down right the first time, or else you'll be on one hell of a flavor experience for the next while