Clinical depression affects 10 per cent of the population. Up to one third of cases are unidentified or hidden at any given time.
In its most severe form it produces profound feelings of hopelessness and despair.
It can also give rise to physical symptoms such as severe loss of appetite, significant weight loss and severe sleep disturbance.
Suicidal ideation or the "desire to end it all" is a feature of depressive illness. Suicide is highest in men and in those over 65.
Significantly, in the light of the recent assisted-suicide case, the rates are rising in women and there is an association with those who are separated or divorced.
In cases of untreated depression, suicide rates of 15 per cent have been reported. Where treatment is successful, the rate of suicide drops significantly. Between 10 and 15 per cent of those with severe depression become chronically ill with the disease despite aggressive treatment.
This week's victim is reported to have tried several courses of treatment without success.
Depression can be successfully treated by using anti-depressant medication, which usually takes effect on the patient within two weeks of commencing therapy.
A minority of patients require more than one type of anti-depressant for successful treatment.
Electroconvulsive therapy (ECT) is used in specific instances of severe depression or disease which is resistant to oral medication.
Psychotherapy, such as cognitive behavioural therapy, is an important option in patients with mild to moderate depression.
