Why did I feel an electric current when touching my light switch?
I have had this happen when touching two items that were both grounded, but not bonded properly.  I used to get it when touching any cable tv coax cables in the house.  The cable company hadn't installed a proper ground to the water pipes.  If I touched the cable and anything connected to the electrical ground I would get a tingling feeling.  Sometimes a painful one.

This happens because ground isn't an absolute voltage.  Ground at my electrical panel and ground on the pole the cable company used differ by enough to be felt.  This can be dangerous if there is a big enough difference.

Check that all cables for TV and phone and such are properly grounded.