chicken or egg question

Told my sister over skype today that I couldn't sleep lately. She said that I'm just stressed out and that my body is reacting badly.

Question is could it be the other way around? Could there be something wrong with my body that's making me vulnerable to stress?

When a doctor says that I've got a hormonal imbalance due to stress, can he not also say that I am stressed because of the imbalance?

Or am I over analyzing this again? Am I just adding more stress by thinking about it?

Ok. I'll stop. And try to get some sleep.