Severe and unrelenting clinical depression; the term depression is generally used over melancholia in diagnosis.
Example: A woman is chronically unable to experience pleasure or to sleep after 4 AM; she finds herself unable to eat and has lost 30 pounds.
Grinnell, R. (2016). Melancholia. Psych Central. Retrieved on February 16, 2018, from https://psychcentral.com/encyclopedia/melancholia/