For the last month, Gabrielle has felt lethargic and has been unable to get out of bed in the morning. She has withdrawn from friends and family because she feels worthless and unlovable. Gabrielle is most likely suffering from

The answer is major depressive disorder (MDD).

Explanation:

This disorder is characterised by a persistent negative mood, which may involve low-self esteem, loss of interest in any type of activity, feelings of loneliness and constant pain.

MDD is usually treated with therapy and medication. It is believed to be caused by a combination of biological, social and psychological factors.