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Sorry to hear your fish is sick
I'm afraid we can't get to the root of the problem without more information, but you should do an immediate large water change (at least 50%; 75% if you can), making sure the new water is warmed and dechlorinated, and see if that improves things; good, clean water is the best first aid for fish. And please don't touch the fish; it's stressful for them and could make things worse.
After that, could you post; the size of your tank, how long it's been set up, what other fish you have, plus the results of any water tests you've done, including pH and hardness, if you know them, please.
That might help us work out what's happening.