The gourami Iridovirus causes the fish to go off its food, develop sores on its body and die after a week or two of showing these symptoms.
If your fish is having trouble swimming and floats up when it stops swimming, it could have air in its intestine or it could have a swim bladder problem. Air in the intestine is the most common cause.
You need to check the fish's poop and see what looks like. If it's white and stringy then the fish has an internal problem (internal protozoan or bacterial infection).
Dwarf gouramis also carry Fish Tuberculosis (TB) and this can cause them to bloat up suddenly (overnight), stop eating, do a stringy white poop, and die within 24-48 hours of showing these symptoms.
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There is no cure for Fish TB or the gourami Iridovirus.
The Iridovirus is a virus and the only thing you can do is keep the fish well fed with a variety of different foods to help boost the fish's immune system. Keep the water temperature warm (26-28C) and stable. Keep the tank clean with regular water changes and gravel cleans. And treat any secondary infections that appear.