SOME Northern Rivers residents may be struck down with a case of friggatriskaidekaphobia today, as Black Friday and the full moon coincide.
The condition is a fear of Black Friday - and yes, it's real.
Lismore psychologist Sue-Ellen Taylor hadn't heard of the phobia before but wasn't surprised.
In fact, several of her patients cancelled appointments for today out of superstition.
"I'd say many people with the condition probably have obsessive compulsive disorder or another pre-existing condition," she said.
"It could be a family thing too. In some families there may be a strong tradition of superstition about the day.
"I saw a lady who had a cross-generational phobia of rats (musophobia) passed on from her family living in Sydney during the plagues of the 1930s. We managed to improve things for her."
Ms Taylor said the most common phobias she encountered were rats, spiders (arachnephobia) and germs (mysophobia).
While most people don't experience friggatriskaidekaphobia, she said a degree of caution surrounding Black Friday was common.
"On Black Friday I think people operate more conservatively and they may perceive the day to be more risky due to superstition," she said.
"The level of fearfulness is down to the limbic system in the brain, which looks after us and keeps us safe.
"The fear has become sort of a cultural tradition."
Ms Taylor said she does not have any qualms about Black Friday and it would be business as usual.
Black Friday's origination is debated, with some claiming it marks the US financial crisis of 1869.
Others say it relates to a day of shopping where retailers historically marked profits in black ink and losses in red.