Psychiatry has two widely used classificatory systems that provide definitions of "clinical" states of such emotions as differentiated from "normal" states - the World Health Organisation's International Classification of Diseases and the American Psychiatric Association's Diagnostic and Statistical Manual (DSM).
The boundaries are not absolute and, in recent decades, the DSM in particular has been criticised for expanding the boundary of clinical states into essentially normal domains.
Degrees of depression
Clinical depression is distinguished in such diagnostic manuals by a number of parameters including severity, duration, persistence, and recurrence.
More severe depressive disorders are accompanied by the individual experiencing gravid depressive symptoms (such as suicidal preoccupations), by distinct impairment (such that it prevents them from going to work) and lasting more than two weeks.
Although severity is an important thing to consider in depression, we prefer to distinguish by depression type, not just severity. Depressive disorders can be divided into two types - melancholic and non-melancholic conditions.
The latter is a diverse group that could reflect the contribution of severe life events, such as being humiliated by a partner or a personality style that predisposes someone to depression.
Such personality styles include being an anxious worrier, sensitive to judgement by others, being a perfectionist, having intrinsically low self-esteem, being profoundly shy or having a low sense of self-worth since childhood.
In contrast, melancholic depression is better positioned as a disease, having rather specific clinical features, a strong genetic contribution, biological underpinnings and responding only partially to counselling or psychotherapy but well to antidepressant drugs.
During melancholic depressive states, the individual lacks energy, experiences little pleasure in life, is physically slowed down, and tends to feel much worse in the morning.
Extremely severe melancholic depression may even include psychosis, though importantly this is normally very responsive to appropriate medical treatment.
The bipolar disorders are also better positioned as "diseases". We now distinguish bipolar I (previously manic depressive illness) and bipolar II conditions - by the extremity of the highs.
While both bipolar I and bipolar II are characterised by swings from high to low moods, in bipolar I the highs (mania) are more extreme and can include psychosis or hospitalisation.
Highs (hypomania) in bipolar II are less extreme and will never include psychosis or a need for hospitalisation. While it's normal for everyone to experience periods of happiness in their life, the highs experienced in bipolar are distinctly different.
The individual loses day-to-day anxieties, feels bulletproof or invulnerable, is excessively talkative, grandiose, creative, needs little sleep without feeling tired, is indiscreet, spends money on things that subsequently cause financial difficulty and may become sexually indiscreet or possibly aggressive.
It's normal for everyone to feel anxious in a variety of situations. Some people might feel anxious going to a party where they don't know many people, for instance, or giving a speech.
The difference between normal anxiety and an anxiety disorder is when the anxiety is so persistent it stops you doing things you want to, or persists even when all logical reasons to be anxious are absent.
Generalised anxiety disorder, for instance, involves chronic worry without a definitive cause and social phobia involves a fear of talking to or being around others.
There are many different anxiety disorders, and it can be difficult to distinguish when normal anxiety starts to become a problem.
Awareness and increase
There are two possible reasons why there has been an increase in these conditions.
First, more people are willing to talk about their experiences, as the stigma of these conditions is slowly decreasing. And changes to criteria in diagnostic manuals have effectively classified some "normal" states as clinical conditions.
But being diagnosed with a mood or anxiety disorder can be a stressful experience itself. The reaction generally depends on how well the person relates to the diagnosis, whether or not the diagnosis was something anticipated and whether or not they expect a diagnosis and adequate treatment will improve their life.
The vast majority of conditions can be treated either psychiatrically or psychologically, but finding the right treatment, while ultimately rewarding, can also at times be frustrating.
It's our opinion that Australia is ahead of many other western countries in having destigmatised mood disorders, and the stigma and negative consequences linked to seeking help has reduced considerably.
Unfortunately, this doesn't mean that stigma is completely eradicated. Some employers may take advantage of knowing that an individual has a psychiatric condition. And the declaration of any condition can prevent people obtaining income protection, and even travel insurance.
But that shouldn't stop people from seeking help when they feel their emotional health is at risk.
* Gordon Parker is an expert in mood disorders, founder of the Black Dog Institute and Scientia Professor at the University of New South Wales. He receives funding from the National Health and Medical Research Council and Department of Health and Ageing. Amelia Paterson is a research Assistant at University of New South Wales and does not work for, consult to, own shares in or receive funding from any company or organisation that would benefit from this article, and has no relevant affiliations.