Friggatriskaidekaphobia is extreme fear about Friday-the-13th, so much so that the believers refuse to step out on that day.

A study published in the British Medical Journal in 1993 pointed out that the risk of road accidents went up by 52 per cent on Friday the 13th, as compared to any other Friday.
"It's been estimated that $800 or $900 million [US] is lost in business on this day because people will not fly or do business they would normally do," said Donald Dossey, founder of the Stress Management Center and Phobia Institute in North Carolina.
Source-Medindia