Depression was a form of mental disorder.
In the Kübler-Ross model (commonly known as the five stages of grief), depression was the fourth stage. (PROSE: Shroud of Sorrow)
In December 1989, Ed Morgan was admitted to a mental asylum with severe depression and agoraphobia. He was released in January of the following year. (TV: Ghost Machine)
Amitriptyline was a drug used to treat depression in the 1950s on Earth. (AUDIO: Submission)