Remember that the more you push these thoughts away, the stronger they will come back at you. Try finishing the thought, or the scene. See what happens. Maybe write it down and read it aloud. Following this thread will eventually lead you to an outcome. You can decide whether this is irrational once you let the fear speak out. Then, instead of questioning it, you can prove it otherwise and it will be silenced because you had already given it a chance to play out its hypothetical outcome.