While to most of us 13 is just a number, there are some people that consider it to be a bad omen. This is the reason office and residential towers often skip having a 13th floor altogether. However when the 13th happens to fall on a Friday, the fear factor escalates to a whole new level! Today happens to be the first of the two fearful 'Friday the 13th's' that we will have to encounter in 2013!

Most of you are probably shrugging this off and just thankful that the weekend is finally here, regardless of date. However there are over 20 million Americans and probably scores more worldwide that suffer from friggatriskaidekaphobia. Derived from the words 'frigg', the Norse goddess whom Friday is named after and 'triskaidekaphobia', the irrational fear of the number '13', their symptoms range from mild anxiety to a nagging fear that something bad is going to happen to even a full-blown panic attack.

Many that suffer from this phobia happen to be employed in professions like construction or ship building, which are fraught with injury risk, which may be the reason they get nervous and fear that their chances of getting hurt are exacerbated when the 13th happens to fall on a Friday.

While nobody knows for sure why the combination of this date and day became so feared, there are numerous theories.

It begins with the irrational fear of the number 13 that some Triskaidekaphobiacs seem to have regardless of what day it falls on. Thomas Fernsler, believes that it's all to do with the position of 13 which follows the nicely rounded 'safe' 12.

The Associate Policy Scientist from University of Delaware says that people often perceive 12 to be a complete number - there are 12 months in a year, 12 zodiac signs, 12 tribes of Israel, 12 apostles of Jesus . . . so on and so forth. Therefore, the number right after that seems incomplete and therefore, deemed unlucky.

Folklore historian historian Donald Dossey , traces the fear all the way back to ancient times, when the Vikings inhabited Scandinavia. 12 gods were having a dinner party at Valhalla, the Viking's mythological heaven. Suddenly, an uninvited '13th' guest, the mischievous god Loki walked in and instigated Hoder, the blind god of darkness to shoot Balder, the god of joy and gladness.

As for Friday? That, happens to be rooted in ancient mythology and religion - Per the bible, Jesus was crucified on a Friday. Though the date is not believed to be the 13th, it was following the Last Supper, which happened to be attended by 13 men that included Judas Iscariot, the apostle that betrayed Jesus. Other biblical scholars maintain that this was the day when Eve tempted Adam with the forbidden fruit - Again, the date is a little hazy. The one bad event that is believed to have happened on Friday the 13th, was the slaying of Abel by his brother Cain (The sons of Adam and Eve).

So how bad is the fear? Experts estimate that businesses lose between $800-$900mm USD on this day because people avoid traveling, going to work and even, shopping! Do you consider Friday the 13th unlucky or are you among the minority that believes that it brings good fortune? Be sure to let us know, by adding your comments below.

Resources: shorenewstoday.com, urbanlegends.about.com, nationalgeographic.com, timeanddate.com