Those of you old enough to remember the 1980's should remember the effect of the last oil price crash. The price of real estate in Texas took quite a tumble and unemployment was rampant. Texas suffered. All the construction workers I knew left Texas for California, Florida and Northern Virginia. Downtown Austin was full of store fronts with plywood for windows.
It is my understanding that the drop in the price of oil was a primary cause of the fall of the Soviet Union, as oil was its primary source of capital.
I think you have a clue of why it is going down now. There are several factions going to suffer. Like us Russia ISIL and several others when the cash flow dwindles.