Galaxy S5 :: Screen Goes Blank But Phone Working

Having a weird issue with my screen. Occasionally, (about 5 times in the last 2 weeks) when I grab my phone, the screen does not come on. I can see the multifunction buttons light up, I can swipe the screen and hear the sound for the unlock, and if I tap on the screen it does not light up and screen stays black.

If I hold power, it does not reboot. if I push home it does nothing, but I can hear that the phone is on, if a call comes through I can hear it ring, and can answer from my home button, but the screen stays black.

I can do a battery pull and phone starts fine. It is as if the backlight is not coming on at all at times, or possibly like a proximity sensor is not allowing the phone to recognize that the screen should be off.

Cannot tell if it is a hardware issue or software issue. I have not changed any software since I got it a few weeks back, some software has updated, but this is happening comepletely at random and always when the phone has been locked.

Phone has never been dropped and is in a case and has no screen protector, there is not a mark on the phone at all.

Should I arrange to swap the phone? should I contact my carrier?