Have you done a head count on the inhabitants of your tank? If everyone is accounted for, he may have eaten a stone or pebble by mistake or may have sucked in some air looking for a way to escape. Not much you can do with that but let it settle out itself.
Ribbon eels ( including Ghost ribbons) do best on a live diet in my experience so you might want to try adding a live shrimp or live fish ( i.e Molly, Guppy, Damselfish, etc) so if he didn't already eat one of it's tankmates, you might try one of these after the bump settles out.