To answer this, I am going to assume that this is a fairly new house, that you are refering to sheet paneling, and that it was installed in typical fashion, none of which is cetain to me from your post, so my advice may be worth almost nothing here.

Paneling of this type is mormally applied over drywall and secured in place primarily with panel adhesive similar to liquid nails. Then small fiunish nails with colouring matching the panel finish are used to hold it in place while the glue sets up.

Your problem probably comes from a panel that was not nailed well enough or not glued well enough. It is possible that there could be dried glue behind the panel that is now hard and holding it away from the drywall backing. In that case, you woiuld have to remove hte sheet of paneliong entirely to fix things, possible damaging it.

Buyt if you can push the sheet back into place with your hands and it just sags back out again, there is a fairly easy fix. You find some panel finish nails to match. Then you get some Gorilla glue and a large syringe from a crat hobby store. I get them from a Veterinarian also. In the area of the bulge and slightly above it, drill tiny holes in locations that will not benoticed and inject the glue, half an ounce here and there. Then force the panel back against the wall and nail it. You migjht also need to place a block of wood against the room side of the panel and wedge it in place to hold the panel back tight against the SR for a day or so while things cure up.

Excellence is its own reward!