Depression can be triggered by life stressors including pain or loss. Depression is not an emotional condition. Depression is a physical condition.
Let me give you the briefest of courses in depression:
The brain functions by sending electrical impulses from brain cell to brain cell. In order to do this, it must have availability of dopamine, norepinephrine and serotonin. The secretion of these transmitters help each cell to fire sending electrical impulse to the next cell where the process continues.
If you do not have enough of any of these neurotransmitters, the brain does not work properly and thoughts, feelings and behaviors change, sometimes dramatically.
There are several reasons why a person would not have enough of a specific neurotransmitter. Neurotransmitters can be depleted by stress. When cells in the brain (especially key areas like the hippocampus) cannot fire correctly, we develop a series of symptoms that we refer to as depression.
The so called “anti-depressant medications” help replenish one or more of these neurotransmitters (by a process we can discuss at another time).
If the supply of neurotransmitters continues to be lacking, the brain structure itself changes. Patients who are depressed for long periods have different brains from “normals” when seen in PET scan.
Depressed patients actually become depressed more easily and often more severely each time.
This thing we call “depression” also impacts the immune system and makes us vulnerable to specific disease and disorders. Among other diseases, diabetes has been linked to depression.
This is why depression is most often measured by the number of specific physical symptoms like a certain sleep pattern, problems in decision making, problems in concentration, changes in libido and continual-unwanted thoughts.
Both positive and negative events may precipitate a depressive episode since either can be stressful. A person may become depressed over the loss of a job or even when entering into a new marriage. No single stressful event will cause depression to develop in every person. The same type of stressor may lead to depression in one person, but not another.
Thus, a person with a comparatively minor injury can, conceivably, be more depressed than a patient with more serious losses.