We often use the word "depressed" to describe someone who's in a bad mood, having a bad day, or just down on their luck. At one point or another, we all get the blues or feel down in the dumps, but this is only temporary and doesn't last long. However, there are people whose mood worsens, as they go into a downward spiral toward clinical depression.

In Big Think's latest video, "6 Things You Need To Get Right About Depression," Dr. Patricia Deldin, director of the Mood and Schizophrenia Lab at the University of Michigan and a professor of psychology and psychiatry, explains that one of the most common myths about depression is that it’s rare. In actuality, depression is one of the most common mental disorders in the U.S., with major depression affecting three to five percent of people at any given time. Major depression is often characterized by a sad mood and lack of pleasure in once fulfilling tasks and activities — most people also note sleep and energy changes.

However, this does not mean depression and sadness are the same. Deldin emphasizes "depression is an invisible illness, it's not one you can see just by looking at somebody." Normal sadness can occur in response to normal life events, while depression, at least in its later stages, tends to be disconnected from actual life events.

Read the full article "6 depression myths you need to stop believing" at MSN News.