Are you able to give us some additional information so we can maybe help prevent something similar happening again?
Details about your tank? How big is it? How long have you had it? Water parameters? What is your water change schedule? How much? How often?
Details about the fish? How long have you had it? What other fish do you have? Did you try any treatments?
Could it be an issue with overfeeding? What do you feed? How much? How often?
Could it be a pregnancy issue?
Any other information you think might be relevant?