I do this from time to time and even with my phobia it does not stress me in the least. It's simple acid reflux from a few causes:
1. being overly full from food and or drink
2. a week or overly relaxed esophageal spinchter (common in smokers)
3. or GERD (gastro esphophageal reflux deasease).

George Carlin did a funny bit about it in one of his acts
"Geez I almost pu*! Maybe i should not go out under these circumstances"!
It's harmless...nasty tasting...but harmless!