Depression (major depressive disorder) is a common and serious medical illness that negatively affects how you feel, the way you think and how you act.
Depression symptoms can vary from mild to severe and can include:
Feeling sad or having a depressed mood
Loss of interest or pleasure in activities once enjoyed
Changes in appetite — weight loss or gain unrelated to dieting
Trouble sleeping or sleeping too much
Loss of energy or increased fatigue
Increase in purposeless physical activity (e.g., hand-wringing or pacing) or slowed movements and speech (actions observable by others)
Feeling worthless or guilty
Difficulty thinking, concentrating or making decisions
Thoughts of death or suicide
Symptoms must last at least two weeks for a diagnosis of depression.
Also, medical conditions (e.g., thyroid problems, a brain tumor or vitamin deficiency) can mimic symptoms of depression so it is important to rule out general medical causes.
Depression affects an estimated one in 15 adults (6.7%) in any given year. And one in six people (16.6%) will experience depression at some time in their life. Depression can strike at any time, but on average, first appears during the late teens to mid-20s. Women are more likely than men to experience depression. Some studies show that one-third of women will experience a major depressive episode in their lifetime.