Why won't my phone stay on?

[AC Question]

Hi all - I came home from work today, plugged in my phone (which was then at 66%), and took a nap for a couple hours. When I woke up, I pulled my phone off the charger, the screen lit up saying I had a few messages, then suddenly the whole phone shut off. I tried turning it back on to no avail, then plugged it back in. It turned on and off about 6 times before it started charging, and it still says '0%' charge even though it's been plugged in for about ten minutes now. What is happening?? I have the Samsung Galaxy S6. It's 4-5 months old and I've never had this happen to my Samsungs before.