Not sure, OP, if you mean your biggest fears or what scared you most during dream-stage sleep.
For the former: family members get attacked or gravely injured
For the latter, it was a fever-dream when I was in elementary school. I was on a stereotypical-horror-movie-type road in the woods-- at night, storming, lined with barren, menacing trees. And the dream WAS in black-and-white. I heard this faint call, and it grew stronger and clearer; it was "Air-vark! Airrrr-vark!" I froze, wondering what would happen. I heard a crash of brush nearby and looked toward it. The noise came from a small hill, and this giant aardvark rose from behind it, continuing to intone, "Air-vark!" That scared the heck out me.....
I do have infrequently recurring running nightmare of losing my bearings and/or performing poorly on some type of odd/twisting/poorly marked/unusual course.