MacBook Retina screen turns gradually black after turning on

A couple of months ago my laptop slid down from a pretty low chair on the carpet. When it did, the screen turned completely black.

When I leave it closed for a while and open it again, the screen is okayish at first with some glitching vertical and horizontal lines on the right and bottom side. They quickly spread until the whole screen is black and only about half a centimeter thick line on the top side is visible (just enough to see half of the menu bar). The mouse cursor doesn't even go beyond that "visible" line, as if the rest of the screen doesn't exist.

I hooked it up to an external screen and everything works fine.

When I close it, and open it again after 5-10 minutes, same thing happens all over again. If I close it and open it immediately, the screen is still black.

Is this some kind of cable issue or would I need to replace the whole screen?