As many as 10% of U.S. employees who miss work due to on-the-job stress may be absent from work for 21 days or more a month. Almost another quarter may not show up on the job due to stress for as many as 20 days a month.

This is among the highlights of "Mind the Workplace," an in-depth survey of thousands of U.S. workers across all industries by Mental Health America (formerly the National Mental Health Association). The survey queried respondents on a wide range of factors related to their work environments, and found that, despite the ongoing bullish economy, employers are doing little to improve morale at work.

The absenteeism numbers were particularly disturbing. Although the majority of respondents said they either never or rarely missed work due to stress, fully a third reported that they stayed away from work from two to 30 days each month because the environment was so stressful.