Depression is different from a bad mood. Unipolar major depression is caused by abnormalities in brain cells, thought patterns, and behavioral habits that have deep and powerful influences on how your friend is experiencing her life. For example, when you are suffering from unipolar major depression, even happy events cannot cheer you up. When depression becomes severe, every positive experience seems like an exception and every negative experience proves the point that your life is falling apart and your situation is hopeless. Your friend’s depressed mind may be clouded and its contents unclear and scary, almost as if she were being forced to watch a horror movie.
Even after you have heard this, it still may not be possible to understand the experience of unipolar major depression unless you have been through it. Concentrate on being a good listener, and let your friend teach you about her depression.