This is a picture I found on the internet illustrating what happens when you have GERD, more commonly known as Reflux. This when the stomach acid backs up into the esophagus( tube from mouth to stomach). It is all to common to have a patient come into the dental chair telling me that they have tooth  sensitivity and they wake up in the morning with congestion.  They might have really good hygiene but constantly have cavities.  These could be signs of GERD.  I tell them to take a Tablespoon of apple Cider Vinegar every morning.  They have to brush their teeth with baking soda and use MI Paste(super concentrated Calcium gel). This usually clears up the problem.  Just to make sure I send them to a GI specialist.