Your teacher probably just wants you to work on descriptions, and it's easier to describe an emotionally-packed event than a boring/ dull one. Try focusing on the describing the feelings and how the event impacted you...Note the small things that are relevant and stood out to you during the moment. As for horror...Well it doesn't have to be some major event... It could be something small. Like the horror you felt when you realized you left your homework or final paper at home after you've already arrived at school...or something like that. Try focusing on the feelings, and good luck! =]