The four pillars regard fire as XiShen, so you should sleep with your head facing south and your feet facing north.
The four pillars are XiShen, so you should sleep with your head facing south and your feet facing north.
The four pillars are XiShen with gold, so you should sleep with your head facing west and your feet facing east.
The four pillars take water as XiShen, so you should sleep with your head facing north and your feet facing south.