Check for ammonia, nittrite and extremely high nitrate. If it is indeed a swim bladder problem there may be nothing you can do except improve water quality if it is poor. If this is the case you can add plants, particularly floating plants with leaves ABOVE the water's surface, such as salvinia, duckweed or water lettuce. These grow very fast and you don't have to be concerned with water CO2 levels. Perhaps the best thing to do is decrease overall biomass.
Also cory cats by far do much better in shoals of at least 5-7. Kept as a pair it is very likely that they will not live their normal life expectancy.