Depression
Depression is a mental disorder that leads to a lack of interest in activities. It is characterized by restlessness, insomnia [3], sadness, low self-esteem and constant anxiety. Depression often causes a person to be unable to function and perform properly at work, school and even in social gatherings. About 30 percent of children with ADHD are also depressed. In fact, depressed children and adults can also have ADHD and vice versa.
When a child is always sad and nothing seems to excite him/her, that could mean depression. A depressed child definitely means something is wrong, because children are usually happy and excited. A depressed adult can be as a result of past experiences and events characterized by abuse and can also be a symptom of ADD or ADHD.