Depression is a mood disorder characterised by persistent negative thoughts. Medically speaking, depression is more than the sadness many people feel periodically. Common signs and symptoms of depression include chronic headaches, persistent fatigue with an increased desire to sleep or, in some cases, insomnia, an inability to concentrate, feelings of worthlessness, unexplained weight loss or gain, a noticeably changed attentiveness to personal hygiene, reduced appetite and thirst, and suicidal thoughts if the condition progresses. There are many factors that can contribute to the development of depression. There might be underlying biochemical or psychological issues that predispose an individual to depression, or there might be a trigger such as a stressful event, loss of a job, or break up of a relationship.