What psychological term refers to a lack of interest or pleasure in activities that were once enjoyable?

The term that describes a lack of interest or pleasure in activities that were once enjoyable is "anhedonia." Anhedonia is a significant symptom commonly associated with major depressive disorder and other mental health conditions. It reflects a decrease in the ability to experience pleasure, which can severely impact a person's motivation and engagement in daily activities.

In contrast, apathy refers to a general lack of interest, enthusiasm, or concern and may not necessarily involve the pleasure aspect associated with activities. Hypomania, on the other hand, refers to a state of elevated mood and increased energy or activity, which is the opposite of the experience described in the question. Dysphoria is a state of generalized dissatisfaction or unease, but it does not specifically capture the aspect of losing interest in previously enjoyable activities. Hence, anhedonia is the most accurate term to describe the phenomenon presented in the question.