From ewin - A note on depression.
Chronic depression does not kill merely through suicide; your body and mind also take a powerful hit every time it strikes. Depression is exhausting and painful. It shifts the balance of chemicals in the brain, and if it lasts long enough, it can cause damage to the brain, making that imbalance permanent. It's hard on the heart, the glands, the digestive system, it's hell on the immune system, bad for circulation.