Check out TheDepressionPortal.org. It provides clear and concise information about depression (symptoms, treatments, etc.) for those who suffer with the disease as well as for their friends and family who are there for support. Important stuff!
People with serious depression sometimes don't fully appreciate their own state of mind. Friends and family need to be alert to downward spirals and be ready to take action to intervene for the benefit of their loved one. Know who to call. Could be the medical team overseeing the patient or EMT to get the person to a hospital, FAST.