Depression, which affects up to one in six men and up to one in four women, affects the way that some people feel most of the time.
Depression is not just feeling sad, as everyone does occasionally.
Depression can be treated using a combination of medication and psychological counselling.
Depression has serious effects on physical and mental health.
Different disorders that have depression as a key clinical component include major depression, bipolar disorder (manic depressive illness), dysthymic disorder, cyclothymic disorder, postnatal depression and seasonal affective disorder.
Some have clinical depression, but it is often not recognised.
People with depression find it hard to function every day.
Because of this, depression in men is often not picked up by themselves or by others, including doctors.
If depression is not detected, it can't be treated and then it has the potential to become severe and disabling.
Fortunately, the symptoms of depression generally react positively to treatment.
Symptoms such as being overweight or underweight, insomnia or excessive sleep can be signs of depression.
By 2020, statistics gathered by the World Health Organization indicate that depression could be the second major disability in the world.
Restlessness, slowed movements, and mental or physical fatigue may also indicate depression.
Additionally, individuals suffering from depression entertain thoughts of self-harm in the form of either self-mutilation (cutting for instance) or suicide.
If the patient in question is a child, the symptoms of depression may include recurrent nightmares, a loss of appetite, and problems in school with learning or discipline that were not previously present.