Here is an interesting item from 2012 about EHS.
EHS has been known for years and the number of people who are suffering from level 9-10 EHS is increasing dramatically.
Many people with level 4-6 EHS suffer but have not connected the dots that link their feeling of unease, head aches, sore muscles, trouble sleeping, etc. is caused by the high levels of RFR (radio frequency radiation) from WiFi routers, DECT phones, cell towers and in some cases sleeping too close to Smart Meters.
Many people, most people, who have level 1-3 EHS seem not to feel any impact from RFR but they are being hammered by RFR at the same rate as the others and the long term impact will probably be the same. Lots of research being done on this.