Nexus keeps on turning off/won't turn back on

[MitchJMacN]

I've had my Nexus 4 for over a year now. Recently it has been turning off even at a full charge, and won't turn back on unless it's charging, and I have to hold the volume button/power button. It's happened to me several times now, when I'm not using my phone. I don't have any apps that don't seem trustworthy. Any fixes? I have the lollipop update, but I believe it was happening before the update.