I get this often. I believe it is the assumption that something bad has to happen. If you have been doing a lot of good things lately, taking care of your problems, making progress, you have a underlying assumption that something bad has to happen. My therapist said that this is a way that we attempt to control the unknown way in which bad things happen.

This often manifests itself as assuming something physical will happen. My uncle had a cardiac arrest at 42, out of nowhere. The arbitrary randomness of it was very frightening to me, because he seemed to be getting his life under control. There is no scientific basis for thinking that the same will happen to me when I start to get my life in order, but the fear remains.