Major depressive disorder, also known as clinical depression, major depression or unipolar depression is a mental illness that can strike very suddenly, with an obvious change over weeks or months from normal functioning to inability to function well at all.
It was thought that this type of depression has a physical cause i.
e lowered levels of neurotransmitters in the brain and still stands as the the most widely held medical theory, but there is still little direct proof as neurotransmitter levels cannot as yet be readily measured.
Such cases used to be called endogenous depression.
In other instances, depressive illness appeared to develop in response to some stressful life event or significant loss or disappointment and these cases were referred to as reactive depression.
However now it seems that some type of stress can be identified in the recent past for most people who develop depression and there may be no difference in the depth of depression, sign of depression, or the physical symptoms which develop between those who do and do not have some identifiable stress.
And so anyone who develops depression symptom severe enough to disrupt their life is said to have major or clinical depression and some sort of neurotransmitter imbalance is thought to underlie it.
Some people may develop symptoms of depressed mood, hopelessness and tearfulness in response to a very specific life event or stress without the full range of symptoms of clinical depression.
These people may have a condition known as adjustment disorder, it is different to depression and resolves spontaneously once the stress is relieved.
Clinical depression can occur at any age even in children.