If you live with someone, have them flip a coin every night to decide if your mat should be plugged in or not and log it in a private journal. Record your feelings in the morning. After a month, compare your reports to the state of the plug each night.

If you live alone, get 2 more identical cord. Have your mats cord and the unconnected ones going into a box. Blindly label the cords a b and c.

The unconnected ones end there, the real one continues to the mat. Cycle through your cords every evening. In the morning log your feelings and the cord used. After a month see which cord was the connected one and whether your feelings were correlated with that