Deep sorrow and intense state of sadness.
I have books of study by Robert Whitaker, "Anatomy of an Epidemic" It is a "controversial" book because it "investigates the long-term effects of psychiatric drugs, and ultimately a history of science that challenges psychiatry to rethink our current drug-based paradigm of care."
Also, you might like to consider in your research: Allan Horwitz and Jerome Wakefield, book, The Loss of Sadness: How Psychiatry Transformed normal Sorrow into Depressive Illness
Over-diagnosing with psychiatric drugs is not the answer in addressing this normal state of intense sadness, sorrow and deep feelings of loneliness.