The coil carries a capacitance, that capacitance can store a charge even
after the coil is shut down it can actually develop a charge when not
connected to anything. I have had it happen several times, what I did to
correct it, was short the coil out after use. I have had them develop a
charge just by moving them around. At first it's not a big deal but after a
few times it begins to hurt a little...Hahaha so I short them out now before
I move them around, you can put a couple of alligator clips on some lead
wire and just keep the coil shorted when not in use and that will also take
care of it.