Hi,
Electric back massager are supposed to decrease blood pressure by relaxation and increasing blood circulation. Unless the gadget has given you an electric shock, it should not be a cause of increased blood pressure. This might be an incidental finding. There might be some other factors responsible for increase in blood pressure (stress, hereditary, increased cholesterol etc). I would advise you to monitor your blood pressure for 3-4 days, and if still high see your doctor.
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regards
Dr. Gupta