Mental Illness and Work

Has Depression, anxiety, or mood disorder kept you from being productive?
My son was diagnosed with Cancer in Nov 2005 and declared in remission in Oct 2006. I was lost at work during that whole time. I could not concentrate and could hardly function. Speaking with my doctor recently, he said that I was most likely suffering from depression. I was lucky. My boss and coworkers really stood by me. What has your experience been?