from Wikipedia: The fear of Friday the 13th has been called friggatriskaidekaphobia (Frigga being the name of the Norse goddess for whom “Friday” is named in English and triskaidekaphobia meaning fear of the number thirteen), or paraskevidekatriaphobia, a concatenation of the Greek words Paraskeví (meaning “Friday”), and dekatreís (meaning “thirteen”) attached to phobía (from phóbos, meaning “fear”).
According to the Stress Management Center and Phobia Institute in Asheville, North Carolina, an estimated 17 to 21 million people in the United States are affected by a fear of this day making it the most feared day and date in history. Some people are so paralyzed by fear that they avoid their normal routines in doing business, taking flights or even getting out of bed. “It’s been estimated that [US]$800 or $900 million is lost in business on this day”. Despite this, representatives for both Delta Air Lines and Continental Airlines have stated that their airlines do not suffer from any noticeable drop in travel on those Fridays