You are not suppossed to sleep with your head pointing north b/c that is the postion they lay people when they die and it is not that you will die if you do it, but it is suppossed to be bad luck.

The fan and the window one are related and it is b/c if you cool your waist region it can give you the runs. So no it won't kill you. Also drinking cold drinks are thought of in the same fashion, as it will give you the runs too. Or so goes the superstition.