The four most common types of depression

Major depression

A dark mood is all-consuming, with loss of interest in activities, even ones usually pleasurable. One may have trouble sleeping, changes in appetite or weight, loss of energy, and feel worthless. Thoughts of death or suicide may occur. Treated with psychotherapy and medication.

Persistent depressive disorder

A low mood that has lasted for at least two years but may not reach the intensity of major depression. Sufferers feel low or joyless. Other symptoms include appetite and sleep changes, low energy, low selfesteem and hopelessness.

Bipolar disorder

Episodes of depression with periods of unusually high energy or activity. Manic symptoms include: grandiose ideas, unrealistically high self-esteem, less need for sleep, thoughts and activity at higher speed, and ramped-up pursuit of pleasure including sex sprees, overspending and risk-taking. Medication can be very effective.

Seasonal affective disorder

A mood change that emerges as daylight hours get shorter in autumn. Treatment includes light therapy.