Depression is a somewhat mysterious illness which can affect both the body and the mind.
Depression can cause many kinds of upsetting feelings. We used to think unusual Depression was due to some hidden unhappiness or conflict in a person's life. We now know that many healthy people who have no reason to be unhappy become depressed. We now think that most Depression is caused by a lack of one or two special chemicals that carry messages from one nerve ending to the next, like little messengers. The chemicals deliver the message to the next nerve, then jump back to the nerve they came from.