Whereas most diseases are defined by their cause (for example, cancer, cirrhosis of the liver), the disorder of depression is currently defined by a collection of symptoms. You feel crappy most of the time. Nothing seems interesting, and everything seems overwhelming. You have trouble with sleep. You feel guilty and anxious and have thoughts that life isn’t worth living. These are the signs that your brain circuits are caught in the downward spiral of depression. And if you’ve got enough symptoms, you’re diagnosed with depression. There’s no lab test, no MRI scan; it’s just the symptoms.
