Thanks Matt for confirming that I wasn't loosing my mind - exactly that - last winter on the C level the fan would go off in the middle of the night and I too would wake an have to reset.

Last week on the 4th floor, the fan would remain steady but the room temperature would noticeably creep up to make it uncomfortable while sleeping. And of course I'm not usually there in the day / evening.

Just another oddity of the place I guess.