Debbie's father recently passed away, and she had to take off work for funeral. Debbie has always been the very outgoing person, simply made friends with others, and was very careful about meeting every deadline at work. Now that she has returned to work, she appears like different person. She is very quiet, has totally withdrawn from everyone, and has missed two very significant deadlines. Explain how Debbie, people around her, and her physician may characterize this behaviour, and what is causing it.