I just noticed a hot spot under my bathroom tile floor that was not there before What is causing this It's hot when you walk over it?

if there a light fixture under the floor (on the ceiling of the room underneath) the heat will eventually rise.

this is most frequent when there is an incandesent light fixture in an uninsulated floor (like a basement 100w light bulb is left on)

something like 90% of electricity used by a 100w bulb is heat.