another point you could check do the gill lay flush to the body when they close, or is there a redness or swelling one side or the other or both....have you added new fish to the tank, have any other fish shown any signs of this. if you can, isolate it from the main tank asap, then do a couple of big water changes in the next couple of days ...at least 50% more if you can but not more than 75% in any one day ...this will hopefully help in diluting any microbes that are in the water that may be causing the distress in your fish ....this is just a precaution it isnt a grantee...or it may just be that this fish is being picked on ...i have one that sits in the corner with its nose pointing into the corner and hardly ever moves and its been like that for 2 years ,nothing at all wrong with it that's just the way it is ...will keep thinking but we do need as much info as you can give ..water stats is always a help, tank size,is it planted or bare bottomed, filter turn over (how much water passes through your filter per hour)as i say as much info as you can...