My stomach (upper abdomen) feels very, very full and tight. I'm short of breath from feeling so full. My stomach feels distended and fat. I used to be able to "suck in," but even that has become difficult. I feel like my heart is beating outside of my chest. I feel sick to my stomach but not to the point of vomiting. I don't have any acid reflux symptoms (or any of the like) that I have researched. I feel like I have gained 100 pounds in my stomach, but I haven't gained any weight. What could this possibly be?