Generally, a fish that is upside-down and breathing heavily is moribund - actively dying. Unless there is some quickly correctable issue that is causing this (low oxygen perhaps) you won't be able to save this fish. However, damage control then becomes important because if the fish has something contagious, the other fish in the tank are at risk.
This post explains the information we need to try and resolve that for you:
Aquarium Fish Disease Problem Solving Determining the best course of action for a problem with your aquarium can be a difficult task. Even advanced aquarists will often need to seek the help of others for complicated or unique issues. Our intent here on Reef 2 Reef is to offer expert advice...
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