The simplest thing you can do (without resetting everything to default), is to save your work, then create a new painting. When you do, the layer panel will not have any layers in the way, so you can left click on the face of the panel, and then drag it down until you can see the top, or bottom of the panel. If you go to the top of panel, you may right click on it, and reset it's scale. If you go to the bottom, you should be able to drag the resize tab for the length up, until you fit it all back on the screen.
(EDIT) - Just in case, here's a video showing these steps: Video Link
Last edited by Someonesane; 06-09-2012 at 01:05 AM.
Nothing is easy to the unwilling.