Is it possible that electro-sensitivity is a real affliction? Well, it's possible. It's also possible that there exists an anthropomorphic rabbit with a fondness for chocolate. But it's really unlikely. Why is electro-magnetic radiation unlikely to have an impact on your body?
Well, light is EMR, is higher energy than your cellphone and wireless router. You're exposed to visible light every day, all day, in extremely high quantities. Aside from sunburn (caused by energies ABOVE the visible spectrum), you don't tend to suffer ill-effects from light exposure.
You are, amazingly, opaque to visible light. This means you absorb a lot of it, and reflect some of it. You are also opaque to IR and Ultraviolet (and absorbing ultraviolet is why you get sunburn). You are not, however, opaque to and form of radio- which means you absorb very little radio energy. This includes the 2.4GHz signals used by cell phones and wi-fi routers. In fact, if you did absorb the radio energy, wi-fi would be pretty useless, wouldn't it? The energy passes through you with very little effect. In fact, the only way to generate a noticeable effect from microwaves is to set up a standing-wave in a contained space, reflecting the same energy into your target material over and over again (and using a transmitter several orders of magnitude greater than your cellphone). We have devices that do this in our kitchens.
Cell-phones and wifi routers output very low levels of energy. Most of this energy passes through you, with very very little effect- the only effect would be a slight warming (very slight- probably unmeasurable). This energy is of the same variety as visible light, which does get absorbed with no ill effects, but is much lower energy. Ultraviolet light, orders of magnitude more energetic than your radio transmitter does have a negative effect, and each increase of energy beyond that increases the damage. You receive more 2.4GHz EMR from the sun than you do from every cellphone you see in your entire life.
So it is extremely unlikely that anyone is "electro-sensitive". Anyone making such a claim would need to provide pretty solid evidence- like say, a double-blind study? Which brings us back to our opening- so far, every attempt at a double-blind study has revealed no results.