Depression is a serious medical illness that involves the brain. It’s more than just a feeling of being “down in the dumps” or “blue” for a few days. For people with depression, the feelings do not go away. Symptoms can include sadness, loss of interest or pleasure in activities you used to enjoy, change in weight, difficulty sleeping or oversleeping, energy loss, feelings of worthlessness, thoughts of death or suicide
Click here for more information. http://www.nlm.nih.gov/medlineplus/depression.html