intermittent shadow across part of macbook air screen

Over the past 24 hours I have been experiencing issues with my screen, usually in the pattern described below:

1. flickering

2. going a little dark at random, as if I've reduced the brightness (though I haven't) or it is inactive (although it's not), sometimes the whole screen and sometimes just half of the screen

3. part of the screen goes dark - a shadow appears in the bottom quarter of the screen (sometimes to the left, sometimes the right)

4. sometimes this spreads so that the screen goes completely black

5. screen comes back to life after approximately 5-10 seconds or so

It's happening with increasing regularity, currently approximately once every 15 minutes, and so I've now just about managed to take some photos using my phone (excuse poor quality!):

(I realise that second photo is upside down, I have no idea why and can't work out how to change it!)

For reference, I am using a mid-2013 13 inch MacBook Air operating OS X Yosemite. It was purchased in April 2014 and hasn't been dropped / mistreated / had particularly heavy use. I didn't purchase an extended warranty.

I'm really just looking for ideas on what is going on / how it has happened / if there is a quick fix (wishful thinking, I know!). I have booked a Genius Bar appointment, but I couldn't get one for 6 days. As the issue becomes more frequent, it becomes more and more disruptive to my work - at best it is distracting but at worst it could put me out of action completely!

Thanks in advance for any help that comes my way 🙂