My husband and me enjoyed many a summer Sunday afternoon stroll around the city canals near the convention centre during the 90s when we lived in Brum and then on one occasion on arrival back at home we both experienced crippling headaches for quite a while, our symptoms were identical. During our search for a possible explanation we remembered lingering under a low towpath bridge under which passed a very heavy high voltage cable (could have been 10,000 volts) - so did that cable emit magnetic radiation that affected us both?
We didn't linger near the cable again.