As with exposure to ‘anything’ sun, pollen, pharmaceuticals, there will be a certain percent of population that is ‘sensitive or hypersensitive’ to wifi / emf frequency. I am definitely sensitive with my husband doing his own control experiment by holding his wifi phone behind by head without my knowledge and me In pain from a piercing wave going through my head. Why is it that it must be all or nothing. There are those who will never be sick from wifi/ emf and those of us who live with it everyday.
Have you ever felt more awake after using Wi-Fi or even struggled to sleep through the night? Reports of these phenomena have been frequent and even prompted a study in 2007 that evaluated low-frequency modulation from cell phones and its impact on sleep. Participants were exposed to the electromagnetic signals from real phones or no signal from fake phones. Those exposed to the electromagnetic radiation had a significantly more difficult time falling asleep and changes in brainwave patterns were observed. 
And David Carpenter, M.D., director of the Institute for Health and the Environment at the University at Albany, says that while exposure from a single router in your home may be small, the risks could be greater in places that have dozens of laptops and routers working at the same time—such as school classrooms. Phillips notes that children’s developing bodies may be more vulnerable to all forms of radiation from devices.