I have the black stripe I the bottom of my screen, but it's getting better as I'm searching for an answer. I have a weird idea - maybe it's because I haven't used my macbook for a couple of months? No idea what exactly happened, it never fell, neither was it left on the sun. The fact is that the stripe is slowly vanishing.
So don't hurry to bring your macbook to a repair shop - just wait and see if it gets better.