The close connection between mental disorders (especially depression) and stress has been known for a long time. Stress is a topic that plays an essential role in the research of mental illnesses from a neurobiological and psychological point of view.
Stress ensures that we and our body are suddenly put on alert for a longer period of time. We are alerted because we evaluate something as a danger. What one person perceives as stress another person can see in a relaxed way.
The physical reaction is that cortisone is released by the adrenal cortex (an organ of the human body), making our organism alert, ready to flee and fight.
This stress response is necessary for us to survive. It becomes a problem when it jumps off frequently for no reason or lasts too long. It can often be observed in mentally ill people that the stress reaction is no longer flexible and adapted to the situation.
Stress can also become a mental illness. The best-known diagnosis is anxiety and it often coexsists with depression.