For myriad reasons, Friday the 13th - today - brings out the skittish in many of us.

You may not typically be the person to shrink at the sight of a black cat or hop along the sidewalk avoiding the cracks. But according to the Stress Management Center and Phobia Institute in Asheville, North Carolina, an estimated 17 to 21 million people in the U.S. are affected by a fear of this day.

Dr. Donald Dossey, the founder of the institute, told National Geographic News several years ago that "It's been estimated that $800 or $900 million is lost in business on this day because people will not fly or do business they would normally do."

The urban legend experts at Snopes.com dug into several theories on why Friday the 13th is so feared.

We want to know if you have any Friday the 13th-induced phobias? What are they?