A healthy mind means a healthy body. This is an old saying but true. A 2008 UK survey of medical issues found that psychiatric illness was the second most common cause of loss of licence in civil commercial pilots.
Psychiatric disorders mean problems with operating machinery, especially aircraft or engineering. They include depression, anxiety, schizophrenia, bipolar disorders, substance abuse and alcoholism.
They are also unpredictable and can cause inappropriate and/or irrational behaviour and impaired decision-making. Obviously a threat to safe aircraft operations.
Stressful conditions at work or while you are flying can also change your reaction to different situations.
Look for these signs in your work mates and be aware that their behaviour can change very quickly. And see the Stress section for more information.