An estimated 20 million people suffer from a fear of Friday the 13th, according to a study by the North Carolina Stress Management Center and Phobia Institute. The phobia, known as friggatriskaidekaphobia, is fairly common. The word comes from Frigga, the name of the Norse goddess for whom Friday is named, and triskaidekaphobia, or fear of the number thirteen. (Also known as Friggaphobia). Beware of the friggaphobes.