Pandora summed it up perfectly. I can't stress enough, if he starts acting a lot differently -- especially listlessness or loss of his regular appetite, act within HOURS if you can to fight it with medication. A bacterial infection can overwhelm a fish in 24 hours, and it's very hard for them to recover once they pass a certain point.
That said, triggers are tough as heck, and they usually just shrug off any minor scratches. Make sure your water parameters are good - nitrates and phosphates low, PH 8.0-8.3. Also, increase his feeding -- I always do that as an insurance policy. If you feed him 5 times a week, feed him 7 until he gets over this. If you feed him 1 meal a day, feed him 2 small meals instead. Just to try to get a little extra good nutrition in him to battle any potential infection (don't let the water get fouled though -- keep an eye on your tests). Then go back to his regular schedule once it is obvious that he is in no danger.