If you have a medical condition you are far more likely to have depression than someone who doesn't.
Depression is a biologically based disorder that can be treated.
And treatment improves more than your mood. It can improve your physical health, too. And, of course, feelings such as sadness are part of life. But it is never normal to be depressed for long periods, usually defined as two weeks or more. Depression is a treatable, biologically based illness caused by chemical imbalances in the brain.