My toshiba 36A50 is having a picture problem.

I have a toshiba 36A50 and it has begun giving me some problems with the picture. it started out with a bouncing line across the bottom of the screen, it has not gotten to the point where I lose about 2" of picture. But the picture is not gone completey, it has been sort of squished from the bottom up. after a good whack on the top of the tv, the picture returns fine. Any ideas what I am dealing with here, and is it something worth fixing?