I hate when I worry about stuff I can't control

Sorry if I haven't been my usual fun self in the past day or so but I got some difficult news yesterday at work and for some reason I don't deal very well with things like this.
Some background, I have a great job that I like and I do well at. I am an outside vendor servicing a major insurance company. I'm sort of a local go between for two companies that have a quarter of a billion dollar yearly account. I enjoy what I do and think that I do it very well. My operation has been used as a model for others across the country. In fact my job was one of the few spared during the restructuring of our department during the recession. My point is this, I have a vested interest in making sure that my job stays the same and right where it is.
Yesterday I found out that my manager since 2004 took a different job in the company. I know that he had been looking at doing something but I was shocked that this seems to have been a demotion not a promotion. This creates the worry. I hate when this happens because I have this terrible internal worry mechanism that I can't seem to turn off that makes me run over all the worst case scenarios when something like this happens. I hate it and intellectually I know it's irrational but I still worry. Why would my manager take a demotion to move elsewhere? Why wouldn't he tell me? Is our department being disbanded? What will happen to me and my customers? What will happen to all I have built here? Why this? Why now? Why me? I can't control any of this but yet I worry.
I hate it but I just can't seem to stop it. Arrrrghhhh!

-Doc