We had a house guest for a while that complained the WIFI caused them to have headaches (whilst merrily holding a mobile phone to their ear for an hour or more every day).
I turned the router off, and about half an hour later they said they were feeling much improved. A quick check on the wifi analyser app showed we were still in the middle of 7 other networks from the various neighbours houses.
Later that night I stuck a strip of black electrical tape across the blinken-lights on the router and turned it back on. Success - no more headaches reported, and available internet for the rest of us!