I'm not in the USA, so I don't have access to Discovery Health Channel. But it certainly is an interesting topic. A look at the Discovery Health Channel website's TV schedule for yesterday, suggests that you might have seen the following documentary: Bipolar Mysteries
, which has the following description: "In this hour, we follow four families raising children diagnosed with Bipolar Disorder."
If that is indeed the page for the documentary you've seen, then you might still get a chance to watch or record the whole documentary. According to that page it will be aired again on 10/16/10 at 3:00 pm and again on 10/19/10 at 3:00 pm.
I'd be interested in hearing more, if you get a chance to watch the reruns.