Contrary to popular belief, depression can not be simply defined as a period when someone is ‘feeling sad.’ There are a multitude of nuanced symptoms that can appear (often at the same time) when an individual is dealing with depression. Referencing the DSM-5: Diagnostic and Statistical Manual of Mental Disorders the following symptoms are indicators of depression:
Persistent sadness, anxiety, or feeling of emptiness most of the day, nearly every day
Decrease in interest or pleasure in almost all activities nearly every day
Binge eating/weight gain or anorexia/weight loss
Sleeping too much or experiencing insomnia
Fatigue, lethargy
Feeling restless or inordinately slowed down
Feelings of worthlessness or inappropriate guilt
Trouble concentrating and remembering
Feeling suicidal
There are other markers that physicians will take into account when evaluating a diagnosis, however these are starting indicators that something may be out of order. Additionally, the term ‘depression’ can be categorized in many different ways depending on how it manifests.
A common line of thinking is that depression is caused by a distressing event in an individual's life or that it is entirely genetic. While it is true that depression can arise out of unfortunate circumstances and be partially genetic, there are a variety of other reasons that someone can be experiencing depression. Research indicates that depression is a combination of genetic, neurochemical, physical, and environmental factors; any of which can be out of the normal range and contributing to a depressed mood.
Biochemical factors - Decreased action or production of neurotransmitters (messengers in the brain) can result in side effects of sleep problems, binge eating, irritability, low mood, or fatigue. Hormones are also closely linked with depression, and an imbalance in essential hormones can result in a multitude of depressive symptoms.
Physical factors - Oftentimes depression is not the only issue a patient is dealing with. Comorbidity -- the presence of two or more diseases simultaneously in a patient -- is very common for patients diagnosed with depression who may also have anxiety, eating disorders, chronic pain, and any number of other conditions.
Psychological factors - Stress, the loss of a loved one, and other traumatic situations can trigger a depressive episode. Individuals who suffer from social isolation or a lack of support are more prone to losing their sense of ‘normal’ when an incident occurs.