Why is my Nexus5 screen turning off on it's own accord

[AC Question]

At first it wasn't happening that often but now it happens a lot, 15-20 times a day. The screen will turn off and not be able to be turned back on unless I restart the phone. I know it's just the screen because my music can still be running whilst this happens. I've been using it when it's happened a few times and it just goes out of nowhere with a bunch of lines down the middle of the phone and then just goes black, but it does still have some backlighting (not completely off/dead). It's really frustrating and I want to know if it's hardware or software, if hardware would likely replace it.

 

[belodion]

It sounds like hardware to me.