"Functional" or "psychosomatic" symptoms, e.g. a flu-like malaise, aches and pain and fatigue, are major features of major and in particular of melancholic depression.
Maes, Michael·Neuro endocrinology letters·2009
This study looked at whether depression and ME/CFS share similar physical symptoms like fatigue, muscle pain, and feeling like you have an infection. Researchers found that people with severe depression often experience these "body-centered" symptoms as a major part of their illness. The findings suggest that doctors should pay more attention to these physical symptoms when diagnosing and treating depression.