Iphone 5s died overnight?

[Ipad Now]

I had about 70% or more battery life but when I woke up about 8 hours later it was dead.
The way I revived it was holding power button and home button at same time while I had it charging. It came back on and had that same 70% battery, so it wasn't the battery.
Any idea what it was? Has anyone else expiereinced this?
The only thing different I did was download a song from iTunes.

Thanks

 

[Ipad Now]

Nothing?