Undefined dread has no edges, so it expands to fill whatever room it is in. Written down, it has to become a sentence, and sentences end.
There is a version of this exercise that helps and a version that doesn't. The one that helps runs to a conclusion: and then I would do this, and then I would ring her, and then we would manage. The one that doesn't just loops.
Give it paper, give it ten minutes, and give it a stopping point. Most catastrophes look considerably smaller in your own handwriting than they sounded in the dark.