What the Friggatriskaidekaphobia?
This Friday, May 13th, millions of people will be too scared to leave their home. Why? They all suffer from a fear of Friday the 13th, known as friggatriskaidekaphobia or paraskevidekatriaphobia.
Fear of Friday the 13th is suffered by approximately 17-21 million Americans, according to the Stress Management Center and Phobia Institute in Asheville, N.C. The phobia is referred to as friggatriskaidekaphobia, a 99-year-old word made up of a combination of the Norse and Greek roots words for ‘Friday’ (Paraskeví), ’13’ (dekatreís) and ‘fear’ (phobia).
The fact that so many people are fearful of the day and therefore will not leave the safety of their homes has an impact on local economy. “It’s been estimated that [U.S] $800 or $900 million 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 Asheville, North Carolina.  Of course, that was written back in 2004, so who knows what that total would be today.
So how did Friday the 13th become such an unlucky day?
Dossey, also a folklore historian and author of “Holiday Folklore, Phobias and Fun”, said fear of Friday the 13th is rooted in ancient, separate bad-luck associations with the number 13 and the day Friday. The two unlucky entities ultimately combined to make one super unlucky day.
Dossey traces the fear of 13 to a Norse myth about 12 gods having a dinner party at Valhalla, their heaven. In walked the uninvited 13th guest, the mischievous Loki. Once there, Loki arranged for Hoder, the blind god of darkness, to shoot Balder the Beautiful, the god of joy and gladness, with a mistletoe-tipped arrow.
“Balder died and the whole Earth got dark. The whole Earth mourned. It was a bad, unlucky day,” said Dossey. From that moment on, the number 13 has been considered ominous and foreboding. 
As if to prove the point, the Bible tells us there were exactly 13 present at the Last Supper. One of the dinner guests — er, disciples — betrayed Jesus Christ, setting the stage for the Crucifixion.
Did I mention the Crucifixion took place on a Friday? 
You may have seen signs of this phobia in places like hotels and airports where the 13th floor or terminals have been omitted.
What’s a friggatriskaidekaphobic to do?
You could join The Friggatriskaidekaphobia Treatment Center for their “Anti-Superstition Bash” in Essington, PA
New York psychologist Dr. Robert Fraum, specializing in anxiety, thinks it’s all in our heads.
“We are fearful and look for ways to concertize our fears,” said Fraum. “Culturally, Friday the 13th has taken on an arbitrary meaning. It’s totally irrational. We are sensitized, and it becomes a self-confirming belief.”
Dr. Donald Dossey, author of “Holiday Folklore, Phobias and Fun: Mythical Origins, Scientific Treatments,” thinks he’s found the cure. Once a sufferer learns how to pronounce “paraskavedekatriaphobia,” he said in an interview with NPR, they’re magically cured.
Each year, the 13th day of the month will fall on at least one Friday and up to three. Thankfully, for all those friggatriskaidekaphobics out there, 2011 has only one.
Footnotes ~ References and Further Reading:
 ABCNews ~ Mind Mood Resource Center
 Stress Management Center and Phobia Institute in Asheville, N.C.
[3-4] National Geographic Article “Friday the 13th”
 Urban Legends.about.com