I've had two Bravos and the pH impedence test, and I can tell you what the technicians told me about the "regurgitation button." Regurgitation, as far as they are concerned, is when you actually feel fluid hitting/burning your throat. (Not to be confused with a chronic throat scorching from constant exposure.) Normally, each individual, separate occurrence of reflux is subtle, and not felt. If there is enough to squeeze up that high, and can be felt, that indicates a greater issue than smaller "blips" that only reach the esophagus.
A sour taste in one's mouth can be symptomatic of a couple of things. It could be the result of regurgitation, but it also could be a chronic response to minute quantities bathing the upper airway during sleep, and overstimulating the nerves even when one is upright. Or, it may also be some sort of sympathetic nervous response to reflux impacting nerves somewhere else in the upper GI. In spite of sleeping on an incline and Gaviscon before bed, I always wake up with this sour taste, and sometimes my tongue will be swollen as well. First thing in the morning I wolf down a couple of bowls of cereal to rectify this, but even now, about an hour later, I can still feel a sourness and sensitivity on my tongue. (Other issues, like dysphagia and hoarseness, etc., are always present.)
Now, there's probably a third category of reflux that Joy is alluding to, and that's "volume reflux." Something like volume reflux may actually be a response to nausea, but if it repeats itself with no obvious dizziness or stomach upset, then it's GERD.
Most doctors use the presence of regurgitation to indicate the seriousness of the problem, and, in fact, I was told that the presence of heartburn and regurgitation are two of the deciding factors for the Linx implantation at the Mayo Clinic.