Some people feel they suffer from depression because of occasional brief periods of sadness following certain life events. Usually, we feel sad following events such as loss of a job, end of a relationship, loss of a loved one etc. However, during these periods of sadness or shortly afterwards, we’re able to engage in our routine activities and can still derive pleasure from activities we love. Depression, also known as major depressive disorder, is a mood disorder that involves a persistent feeling of sadness and loss of interest, which lasts for at least 2 weeks. It can last for months, even years, and usually require medical intervention.