Clinical depression is not a single disease and is accompanied by a wide array of physical symptoms. The most prominent is exhaustion. This debilitating state is not relieved by sleep, rest or other positive interactions with the world. It persists right across the 24-hour sleep-wake cycle and continues, unabated, from day to day.
Other symptoms include muscle aches and pains, headaches, disturbed gastro-intestinal function, change in bowel habits and changes in appetite and weight.
Perhaps, most importantly, sadness is not a key feature. One of the most frustrating aspects of spending a great deal of my professional life