Japan's corporate warriors aren't getting enough sleep - and it's costing the country billions.

In the country that gave the world the word "karoshi," or death from overwork, drowsy employees turning up late, taking days off or struggling to stay awake on the job are causing economic losses of about $30-billion a year, according to a survey.

"The idea is to raise awareness of the problem," said Makoto Uchiyama, professor and chairperson of the department of neuropsychiatry at Nihon University School of Medicine, who conducted the survey.

"Not everyone who is sleepy at work is lazy. It's hard to tell your boss that you are sleepy, but ignoring the problem can lead to losses in the long run."

Japanese routinely work long hours, as much from cultural constraints on leaving before colleagues as from volume of work. Suited salarymen napping, often standing up, are a common sight on crowded commuter trains.

The survey questioned 3,075 workers at a chemical company on their sleeping and working habits for a month.

About 37 percent of respondents said they had problems sleeping. They said their efficiency at work was reduced by about 40 percent and reported a high frequency of accidents, lateness and absenteeism.

Uchiyama said other countries may be in a similar situation.

"It may be thought that this is a Japanese problem. But it's not, it's global."