Horizontal grey lines across entire display after VGA external screen disconnect

Hi all,

I have been using an external screen with my Macbook pro from mid 2014, retina display, Yosemite. After disconnecting the power on the external screen the screen on my Macbook started flickering, with broad horizontal lines moving at the low end of the screen. Now it stabilized, but the retina display still shows tight grey horizontal lines across the whole display, regardless of the app I'm using. When connecting to the external screen that screen looks fine, so it seems something went wrong with the retina display after the disconnecting from the external screen. Is there a fix for this, or do I need to contact support? The Macbook is only a year old, so I guess I'm within warranty.

Anna Sara