People with depressive illnesses don't all experience the same symptoms. How severe they are, how frequent, and how long they last will vary depending on the individual and his or her particular illness. Here are common symptoms people with depression experience:

•    Difficulty concentrating, remembering details, and making decisions
•    Fatigue and decreased energy
•    Feelings of guilt, worthlessness, and/or helplessness
•    Feelings of hopelessness and/or pessimism
•    Insomnia, early morning wakefulness, or excessive sleeping
•    Irritability, restlessness
•    Loss of interest in activities or hobbies once pleasurable, including sex
•    Loss of pleasure in life
•    Overeating or appetite loss
•    Persistent aches or pains, headaches, cramps, or digestive problems that do not ease even with treatment
•    Persistent sad, anxious, or "empty" feelings
•    Thoughts of suicide or suicide attempts
Are There Different Types of Depression?
There are a number of different types of depression including:
•    Major depression
•    Chronic depression (dysthymia)
•    Bipolar depression
•    Seasonal depression (SAD or seasonal affective disorder)
•    Psychotic depression
•    Postpartum depression
•    Substance-induced mood disorder (SIMD)
Are There Other Types of Depression?
Other types of depression that can occur include:
•    Double depression -- a condition that happens when a person with chronic depression (dysthymia) experiences an episode of major depression.
•    Secondary depression -- a depression that develops after the development of a medical condition such as hypothyroidism, stroke, Parkinson's disease, or AIDS, or after a psychiatric problem such as schizophrenia, panic disorder, or bulimia.
•    Treatment-resistant depression -- a condition that doesn't respond to treatment with antidepressants, and may be longstanding or chronic. For chronic treatment-resistant depression, electroconvulsive therapy (ECT) is sometimes the treatment of choice depending on the nature and severity of symptoms.
•    Masked depression -- a depression that is hidden behind physical complaints for which no organic cause can be found.
Warning Signs of a Depression Relapse
A depressed mood during most of the day, particularly in the morning
Fatigue or loss of energy almost every day
Feelings of worthlessness or guilt almost every day
Impaired concentration, indecisiveness
Insomnia (an inability to sleep) or hypersomnia (excessive sleeping) almost every day
Markedly diminished interest or pleasure in almost all activities nearly every day
Recurring thoughts of death or suicide (not just fearing death)
A sense of restlessness or being slowed down
Significant weight loss or weight gain
A key sign of depression is either depressed mood or loss of interest in activities you once enjoyed. For a diagnosis of depression, these signs should be present most of the day either daily or nearly daily for at least two weeks. In addition, the depressive symptoms need to cause clinically significant distress or impairment. They cannot be due to the direct effects of a substance, for example, a drug or medication. Nor can they be the result of a medical condition such as hypothyroidism.