We all have our down days.

But down days that seem to linger longer could be a warning sign of depression.  This sign and other symptoms can interfere with the ability to work, sleep, eat, and even get involved in once-enjoyed activities.

More than 20 million Americans suffer from some form of depression, according to the National Institute of Mental Health. ABCNews.com has shared some of these stories, from post-disaster depression to postpartum depression.

If you or someone you know suffers from depression, there are ways to get help.

Join ABC News’ chief health and medical editor Dr. Richard Besser for a Twitter chat Tuesday, September 13 at 1p.m. EST on depression. The chat will include discussions on warning signs, living with depression, helping others cope, and where to go for help.  ABC News.com’s OnCall+ Mind and Mood section features answers to basic questions on depression from dozens of experts nationwide.  This resource section includes definitions on forms of depression, prevention methods, and potential treatments for the disorder.

On Tuesday, we hope you’ll get involved in the discussion. Ask questions and share your stories. Use the hashtag #abcdrbchat.

Tuesday’s #abcdrbchat Twitter chat on depression is one in series weekly Twitter chat by ABC News cheif health and medical editor Dr. Richard Besser. The content discussed is informational and does not serve to substitute medical advice from a mental health professional.

For more information on depression consult a mental health professional or call the National Suicide Prevention Lifeline at 1-800-273-TALK (1-800-273-8255).