i used to, back when i'd take bigger hits then i could handle... the only reason i can think is that you're trying everything you can to NOT cough out the hit so you just naturally 'swallow' to like stop the 'need to cough' feeling and you just happened to of not inhaled all the smoke yet.. it used to make me really nasueas if it happened like more than once... and i don't understand how a mouth full of air, ends up making you burp multiple fucking times.. it's like when the smoke hits your stomach, it instantly turns into 5-6 times the volume it was when you swallowed it...

i haven't swallowed a hit in years now... i don't really ever need to cough either.. but if i do, now it's after i've already held my entire hit in for a few seconds, as opposed to when i just barely start inhaling..