Depression is very common among people who have diabetes. The data we have so far is from comparisons between people with diabetes and normal controls. I have not seen any data comparing diabetes with other chronic illness, particularly with some painful, incapacitating conditions like rheumatoid arthritis, multiple sclerosis, etc. We know a lot about the clinical aspects of depression, but its biochemistry is still a big enigma. What we are quite certain of is that many depressions are mostly chemical imbalances in the brain, and not necessarily due to life events or childhood trauma.
Depression can be fatal.
It kills through suicide. Once you convince yourself that nobody is able to understand your problems, that nobody can help you and that life is not worth it, you should know you are in trouble. When you are that advanced, you need to get outside help. Once you start to think about suicide, you should call for help right away. Exercise a lot.