Why is it less problematic to drink the soda pop after the bubbles have all gone away? I was surprised to see that carbonated beverages do not slow down gastric emptying. What they do is alter the location of the stomach contents a bit:
Dig Dis Sci. 1997 Jan;42(1):34-9.
Effect of carbonated water on gastric emptying and intragastric meal distribution.
Carbonated water has long been advocated to relieve dyspeptic symptoms, suggesting that it may alter gastric motility via gastric distension. This study aimed to determine the effect of carbonated water on gastric emptying of a radiolabeled mixed meal in eight healthy volunteers. Meal emptying and its distribution within the stomach were assessed with carbonated and still water in a crossover study. Emptying of both solid and liquid, including the duration of the lag phase, was identical for both drinks. However, the proximal stomach contained a greater proportion of solids (74 +/- 7% vs 56 +/- 8%, P < 0.05) and liquids (43 +/- 5% vs 27 +/- 4%, P < 0.05) with carbonated water as opposed to still water. Retention of the meal within the proximal stomach ended with the lag phase and was likely related to proximal distension. In conclusion, carbonated water did not alter overall gastric emptying but profoundly modified intragastric distribution of the meal.
The proximal stomach is the part of the stomach that is closer to the lower esophageal sphincter, which is where acid reflux from the stomach occurs. If carbonated water causes the proximal stomach to contain more food and liquid than usual, that seems like it would contribute to acid reflux. I'll have to look more into it in the future.
In the meantime, when in (nauseated) doubt, set it out. The soda pop, that is.