Panasonic picture shrinks to 1/2" bright horizonal line in middle of screen?

I have a Panasonic 32" (don't know the model number off the top of my head) that I use mainly to watch DVDs in my hobby room while I am working on other stuff. Recently it developed a problem where the picture will get grainly (almost as if it was a VCR and the tracking was off). Then suddenly the entire screen goes black except for about a 1/2" VERY BRIGHT horizontal line across the center of the screen. The only fix I have found is to jump up and down on the floor as this vibrates the TV and temporarily returns the picture to normal. I have produced the problem with 2 different sources so I know it is the TV.

Any ideas what this might be and if it is fixable?

Thanks.

Thanks! Now that I know the term "vertical deflection" I was able find a lot more info out there.

The model number is actually a CT-27D31. If I have time this weekend I may open it up and look around inside. I happen to have a soldering iron sitting right next to the TV! Any advice on finding a cold solder joint?