According to experts, individuals who frequently decline social invitations with excuses such as being "swamped" or "too busy with work" may be hiding signs of a lonely mental health crisis. Other potential indicators include skipping meals, experiencing extreme energy swings, using self-deprecating humor, and unexplained bouts of illness. Dr. Madhukar Trivedi, a psychiatry professor at the University of Texas Southwest Medical School in Dallas, notes that physical symptoms are common in depression, suggesting that individuals may be struggling with their mental health despite appearing to be physically healthy.
https://www.dailymail.co.uk/sciencetech/article-14245505/Subtle-signs-partner-secretly-miserable.html