Poor quality sleep can affect workers’ mood and judgement—and result in serious health problems, reports Fast Company.

Did you lose a day or two of work last year because you slept poorly the night before? You’re far from alone, according to new results from the World Sleep Survey.

The study, which was conducted by researchers at the University of Oxford in collaboration with U.K.-based health care company called Big Health, found that full-time employees in the U.S. lose an average of seven days of work per year due to poor-quality sleep. And those who report that their sleep is of “less than average” quality lose more than 13 days. More than 20,000 people participated in the survey.