I had such as a child. They eventually disappeared but at age 55 returned with avengence. I think they result from iron overload in children. The body allows this iron to oxidise as either hematite Fe2o3 or magnetite Fe3o4. The combination forms magnetite chains which are ferromagnetic and align with the Earths magnetic field and lie in the blood facing north-south. therefore in the arteries and veins of arms and legs if you face east west at night they may readily strike nerves causing discomfort. This maybe better for your feet. Try turning the bed through 90 degrees if possible. Also, if you sleep on a steel sprung mattress the chains of molecules are more evenly spread because the lines of the Earths magnetic field are attracted to the springs. Long term, you can chelate iron oxide by diet but the methods are many and varied.....