Any time you have a fish laying down awkwardly something's wrong. At the bare minimum you have a knife who's got a terrible internal disease; I can't imagine much better for an animal with those symptoms.
It's not normal for it to lay on top, but under would be fine. Unless you have some covering over the driftwood, then that might be a possibility. Check your water parameters. What's your temp at? And observe the CK closely. It may also be sick.