Individuals' experience of mental illness and their mechanisms for coping with it can differ widely, complicating the understanding and treatment of mental health conditions.
And many sufferers hide their symptoms because of the stigma surrounding mental health problems at work, which then contributes to this lack of understanding. The cycle of illness, ignorance and apathy continues.
So it's imperative that organisations in general and HR professionals specifically know how to spot the signs of mental health issues among their workforces.
Employees are taking a lot of sick days
Absence is the most obvious sign of a health problem, but it's rare for people to call in sick and openly cite depression or anxiety as the reason they are not coming into work. Regular short-term absence that isn't accompanied by a doctor's note for a chronic problem could indicate an underlying mental health condition.
Mental illnesses may be cited by GPs on fit notes for employees off work for more than seven days, but the co-occurrence of many mental and physical illnesses means there could be a mental health component to a long-term physical problem that hasn't been disclosed in a fit note.
Grievances have been brought against the organisation
By their definition, complaints signal problems with workplace wellbeing. They highlight distress to an individual caused by the behaviour of another member or members of the workforce.
An employee with anxiety may be bullying other team members. Stress caused by a heavy workload could re-ignite the symptoms of an underlying eating disorder. In other words, grievances and complaints may be causing, or be caused by, poor mental wellbeing.
Employee engagement is low
Employees with little or no job satisfaction aren't motivated to get their work done, let alone complete it to a high standard. They may not like their particular job role, they may not get on with their line manager, they may not feel that their employer inspires loyalty. Or they may have a mental health problem, which is stopping them from getting their work done, even though they have made it into work.
Presenteeism indicates a problem with wellbeing, engagement and motivation generally. And poor mental health could play a role - either by causing or by being exacerbated by low levels of engagement.
The organisation is experiencing poor levels of productivity
Physical illness can lower productivity, just as mental illness can. However if the symptoms of poor mental wellbeing are hidden by employees or not seen by employers then low productivity demonstrated by some members of staff may be blamed on a lack of ability, rather than the fact that they are coping with mental health problems at work.
Staff turnover is high
Whether it's a negative workplace culture, uncompetitive pay and benefits, poor job role design, or poor mental wellbeing - employees leaving organisations in their droves indicates a problem.
Individuals with mental illness may resign because they just don't get better and they need to stop working while they recover. Or they may leave organisations because they feel being there is making them mentally ill.
Whatever the cause, poor mental wellbeing will stop anyone who is experiencing it from working to the best of their abilities.