I do know the feeling of waiting for a scan. Sometimes it overwhelms you. I try to think about other things and put it into my mind that everything is going to be fine. Worrying about the what if's will drive you batty. I prefer to not worry about what I cannot control. I heard a quote years ago when first starting treatments that said, "Keep your mind OFF what you don't want, and ON what you do want". So anytime I start feeling like you are I turn those thoughts off and start thinking about what I want, what my wife and I are going to do. It helps and works for me.
I hope you can get a grasp of your runaway feelings.