The organisation said that depression and mood disorders, PTSD and trauma, eating disorders and psychotic disorders collectively made up the remaining referrals.
The research found 2.4 million workers across Britain were very anxious about sudden changes in their shifts.
The study revealed that Manchester was the least anxious city with only 48 searches per 100,000, followed by London with 59 and Durham with 78.
The survey identified the top anxiety-inducing situations at work, with performance reviews affecting 50% of employees.