Megalomaniak Has never made sense to me but I guess it depends on what 'up' even means.
I always imagine this on a piece of paper:
Then adding the Z axis is like punching forwards and backwards through the paper to add depth:
Often when I add a 3D ground plane I subconsciously start thinking of 2D positional co-ordinates (X/Y) again, but guess that's just a quirk of the brain trying to abstract projections of 3D on a 2D screen.
Conversely, I guess if you already considered the X/Y flat graph to represent the equivalent of a lat/lng position, then Z would absolutely be the 'height'. There isn't a correct answer I spose, and consensus is a pipe dream when everyone is already different: