No idea what was going on with my phone today.
It was in my shirt top-pocket as usual, and I was suddenly aware of my nipple getting very hot
Checked the phone and it was really hot - like the kind of heat that playing games on it causes.
It hadn't received any calls or anything - it was just idle.
Checked battery usage and there was nothing unusual.
No tasks running either.
So no idea what triggered it to suddenly go into over-drive.
Rebooted it and its been fine since.