Depression.
The symptoms of depression syndrome (as opposed to a period where we have a low mood state) can be divided into the following categories:

Motivational: apathy, loss of energy and interest.
Affective: depressed mood, guilt, anxiety, anger.
Behavioural: decreased activity, reduced coping, social skills deficits.
Cognitive: negative thinking, indecisiveness, poor concentration.
Biological: sleep disturbance, loss of appetite, decreased sexual interest.

The cognitive psychotherapeutic strategies are considered to be very effective in dealing with depression.
The main goals of a course of 15 or so sessions would be to relieve symptoms, to help acquire new coping strategies and to modify the underlying cognitive (thinking) structures in order to prevent relapse.
An alternative and shorter approach might focus more toward alleviating the symptoms, and working with self esteem and motivation with hypnosis and self hypnosis. In this case a few sessions may bring noticeable relief.
More information about depression can be found at
http://www.clinical-depression.co.uk/