We all have reasons to feel sad from time to time. Grief is a natural part of life and necessary for healing. Deaths in the family, accidents ad illness, financial losses - all can be a cause for for depression, and if these symptoms go on for a long period of time, the diagnosis is clinical depression.

However, an article on CBS5 talks about new criteria for judging clinical depression:

Now, a new study suggests up to 25 percent of those patients are not necessarily suffering from depression. Instead, they are just reacting normally to a painful loss in their life.

After analyzing 8,000 patients, researchers found extended periods of intense grief may be natural and common in people who have experienced such a loss.

Medicine Net.com lists these symptoms of depression:

• sadness
• Loss of enjoyment from things that were once pleasurable
• Loss of energy
• Feelings of hopelessness or worthlessness
• Difficulty concentrating
• Difficulty making decisions

(And seven more)