What is the most likely diagnosis for a patient showing signs of chronic fatigue, insomnia, and loss of interest in usual activities?

The symptoms presented, including chronic fatigue, insomnia, and loss of interest in usual activities, align closely with the diagnostic criteria for major depression. This condition is characterized by a persistent low mood, anhedonia (the inability to feel pleasure), and fatigue that does not improve with rest. In major depression, insomnia may be present either as early morning awakening or difficulty falling asleep, contributing further to the overall feelings of fatigue and sadness.

The combination of these symptoms over a significant period suggests that the individual is experiencing a major depressive episode. In contrast, anxiety disorders might involve fatigue due to excessive worry, but they typically have more pronounced symptoms related to anxiety rather than the pervasive low mood and anhedonia characteristic of major depression. Adjustment disorder is often a reaction to a specific stressor and usually does not present with such pervasive symptoms without an identifiable trigger. Bipolar disorder involves episodes of mania or hypomania alongside depressive episodes, and the absence of manic symptoms makes major depression the more fitting diagnosis in this scenario.