perhapponism
A perhapponism is a fear of something that may happen in the future, but which is magnified out of all proportion so that it dominates all your thinking.
I keep on having a perhapponism that if I do go on a walking safari in Africa it will be my last. I know it's irrational to think this because the safari guides have all got rifles and there aren't any really dangerous animals where we would be going anyway.