That, plus atmospheric conditions such as thunderstorms and strong winds, in combination with the huge amount of microwave radiation flooding and permeating us all the time — i.e. anything from the electric fields coming off of household devices (e.g. refrigerators, television sets, radios, computers, et al) over cellphone signals (both from the towers and from the phones), WiFi signals (from the wireless internet providers' towers and local hot spots, from household and corporate WiFi routers, and from all the devices that connect to them) all the way up to GPS and other satellites which are constantly bombarding Earth with EM radiation.
All of the above — and especially so in conjunction with certain atmospheric conditions — create very high degrees of ionization. The body's neurology is electric and picks up on that. Trust me, I know what I'm talking about, because I'm extremely sensitive to that stuff, and so is my brother, and so was our father.