Why Do I vomit When Smoking?

Im quite a heavy smoker, and about 15% of the time when I smoke I cough so heavily that Air or something gets trapped with a mixture of Saliva, and When I cough so aggressivly , i have a massive air bubble trapped in my throat/back/lungs and It forces me to swallow, I dont even ask myself to do it, I dont want to do it, but my reflex is just to swallow, alot, swallow after swallow of any saliva thats in my mouth, then after, I go outside , and spit out all the saliva and try to burp best I can to remove the air, but this time it was not enough, my body could not get the burp up and I vomited absoloutly eveywhere, Why does this happen? my Friends call it Golly. why does it happen