Corey,
I had the same exact problem you described about 3 months ago... thin, bloated stomach, darting into the glass, hiding, ect. (Unfortunatly, I lost my fish too)
A few people told me that recently dwarf gouramis have had some sort of parasite going around. Other than that I really have no information besides the fact that you don't have to worry about your other fish if your gourami had the same problem mine did. My problem was specific to that one fish, and didn't affect any of the other fish (besides having to run from him during his "spaz-out" run into glass sessions)