Depression is a common condition. There are many people who have these symptoms or similar symptoms. Unfortunately, they are very serious and cause significant detrimental effects to one's life. At the extreme, suicide is a very real possibility. As such, I would recommend that you encourage your friend to see his or her primary care physician
. He or she may be able to help with various treatments or a referral to a psychologist
The cause of depression is not completely understood. We do know that there is an abnormal balance of chemicals in the brain that can predispose one to depression. Specifically, we know that people who have a depressed amount of serotonin and or norepinepherine are more likely to have depression. As such, there are many medications that increase the amount of serotonin or norepinepherine that have be shown to improve depression. These medicines are known as SSRIs or SNRIs -- common examples include prozac and celexa.
Why do people have these imbalances? We know that early life stresses or significant life changes can cause a change in these levels. In addition, some people have genetic predisposition to these chemical abnormalities. People whose parents have depression are more likely to have it.
Have your friend see his doctor
. Good luck!