Xperia Z2 :: Screen Keeps Fading / Horizontal Lines Appearing

I woke up this morning to find the screen on my Z2 to be very off colour with hundreds of horizontal lines consistently moving down the screen. I haven't damaged my phone in any way recently, why this is occuring.
 
I would put it down to a hardware defect, however when my phone locks itself and I go the unlock it, or if I leave it for a few minutes, the screen will be fine for a few seconds or so, until it gradually fades to a white, then pinkish colour with vertical lines, and then blueish white horizontal lines will begin to move down the phone until it becomes quite impossible to actually use it. I've also just noticed that the lines get much worse when I'm actually using my phone rather than just staring at it idly, so it must be touch triggered or something?
 
I've had this phone since around December after it replaced a lost one, and haven't had any issues so far. I would take it to the phone shop to get it repaired, but I know that will leave me without a phone for 1 - 2 weeks, which just isn't an option. I'd just like to know what the exact issue is before forking out £50 for a new screen.