EVERY ONCE IN A WHILE, MAYBE ONCE EVERY TWO WEEKS OR LESS, FOR ABOUT THE LAST 5 YEARS, I GET A SUDDEN DULL PAIN AROUND MY NAVEL AREA AND FEEL VERY NAUSEOUS AND GET EXCESSIVE SALIVA. I SWALOW AND MORE SALIVA, REPEAT EXCESSIVE SALIVA AND SWALLOWING FOR A FEW MINUTES, THEN IT ALL GOES AWAY. WHAT MIGHT CAUSE THIS?