Default Occasionally very hot when charging wireless

Has anyone had the phone go very very hot while charging? I'm using the official mini charger and back cover for the S5, and the phone has gone super hot (can't hold to my face - but still runs fine) twice in 2 weeks.

The first time I assumed was my fault, as I left it to charge on a bed.
The second time I started charging it at 7%. I pulled it off due to the heat at 51% (no warnings, I just did as a precaution) with adequate space to cool