Working backwards...

Trying to scream/talk but being unable to is often referring to the sense of powerlessness, or having no voice of your own.

The white void is a singularity. It could relate to being alone... or it could relate to being lost. The emotion and focus that came with facing the white expanse is important. What was your initial reaction? What was your first worry about it?

Walking down an isolated road (the word "isolated" just popped in my head. Might be intuition for this...) Were you lost? Were you simply wandering? There is still (though this is the root of the thought) this theme of being alone, by one's self.

In fact, let's address the pivotal moment as a whole. There was a shriek - did you know whose shriek it was? Was the source physically nearby or was it just in the air??? Then you turned and faced an eternal whiteness. (White can relate to many things. Here, it seems as nothingness, but is it a positive nothingness like a blank slate, or is it destructive like having the whole world taken away?) What was your initial thought reaction to the whiteness. You said you were afraid - what was driving the fear???