If you've never been depressed, I wouldn't waist a second on worry about this. By 21 most BP diagnoses have at least been severely depressed. It' s possible, yes, but not the most likely. I have 4 siblings and only one of them is diagnosed. He is a twin and his twin is the healthiest of us all. Maternally there is a very long history of severe depression and paternally we have 2 uncles who were/are bipolar (they are 2 of 5).