Nightmares

Idea

One day, I had an idea. I waited until it was time for me to go to bed, and then I set up a video camera. Just when I was falling asleep, I flicked it on. Then, I sank into my dreams.
The nightmare started out normally - I was stuck in quicksand, the zombies knocked me to the ground. But this time, I stayed in the dream for longer. The zombies shrieked and pulled me along the quicksand. Out of nowhere, ropes flew in and bound me. I was gagged, even though no one touched my head. The zombies kept dragging me until I managed to wriggle out of my bounds and stand up. That's when I realized that they were no longer zombies - they were multiple copies of Priscilla!
They all started talking at the same time. "You must help me, quickly, quickly, I am in the ground, tight, I can't breathe, you must get me out-"
I woke up to my mother shaking me. She looked worried. "Allison! I heard you talking in your sleep. You were saying 'Priscilla...' Who is she?" my mother asked.
"A girl.. in my class." I whispered, sitting up and getting a drink of water.
My mom stared at me. "There's no one in your class named Priscilla..." she said.
I looked at her. The hairs on the back of my neck stood up. My mom smiled sadly. "There was a girl named Priscilla who died a week or two ago. She had a twin, Polly. They died of asphyxiation. They're buried next to each other."
I remembered how they'd been quiet and withdrawn a few weeks ago. They left one morning, dressed in black, and came back with teary eyes. But they wouldn't talk about it.
Suddenly, I realized something.