S7 Edge turned off and wouldn't turn back on

[Steve Swift]

Two days ago my S7 Edge turned off and wouldn't turn on again. The display and the LED indicators remained off, even when I tried charging it, via cable or fast charger. It seemed utterly dead.
But I kept experimenting, as I had nothing to lose.
Yesterday morning, charging by cable came back, starting from 0% (it had been at 45% when it turned itself off, but without display or LED, I couldn't tell the state of the battery).
I let it charge to 40% an tried to boot. It got through some of the initial displays of "SAMSUNG" then froze, making a buzzing sound, and leaving the LED blue. Then the buzzing stopped, but the LED kept pulsing blue.
I left it alone.
This morning, it could be charged again, and it got further through the boot, then froze again.
This evening, the boot completed, but it rebooted before Android finished loading.
Then I realised that it was getting very hot, especially if I replaced the Samsung Flip Cover. I've left this off ever since.
It's still hot at the back, except in the region of the antenna. I can use the phone, but I'm leaving it on the top of a stainless steel bin, which acts as a giant heat sink.

Is there anything I can do to deduce why it is running so hot?

 

[chanchan05]

I think your battery is shot.

 

[Steve Swift]

I would certainly agree with this, but for the fact that it seems to have gone back to normal.
I'm a strong believer in:
Problems that go away by themselves
-come back by themselves.
—Marcy Davis
... so I'll be keeping a watchful eye on this.