This just happened all of a sudden... I'm not entirely sure how to describe this... I'll let the image do the talking!
http://i.imgur.com/Kozlg.jpg

Basically it's like the desktop is just gone there. I can't right click and widgets/plasmoids/panels don't show up on it (they do however, in that sliver of desktop still there at the top). I've tried several things, from restarting X to fiddling around with the Nvidia settings. What's going on here?