I nearly fell over the side of an escalator yesterday, in one of these shopping malls. The drop would have been several floors. I was doing my usual trick of squeezing past stationary folk who stand to one side of the escalator, when a thick-set woman (though it could have been any weight and gender) stepped out into my path and the inadvertent shoulder-charge nearly sent me over the side. I was wearing a backpack, which helped move my center of gravity upwards.
So next time you're overtaking on the escalator, I recommend bending your knees like Groucho, or you could try ringing a bell to warn them someone's coming through.