One: 'I heard a strange scratching at my window all night. In the morning, I saw the marks were from the inside.'
One scary one is 'The old dormitory elevator always groaned. Today, it sang a lullaby.' The sudden change from an ordinary, if a bit concerning, sound to something so much more eerie makes it quite frightening.
I woke up to find a handprint on my window. It was on the inside.
I woke up to a cold hand on my shoulder. When I turned, there was no one there.
She heard a knock on the door. When she opened it, no one was there but she felt a cold hand on her shoulder.
She opened the old wardrobe. A pair of eyes stared back at her from the darkness.
A third story could be: 'I took a photo of the cemetery. When I looked at it later, there was a figure standing behind me that I didn't see when I took the picture.' It gives a feeling of unease as it implies that there was some sort of ghostly or otherworldly figure present at the cemetery that the person was unaware of until they saw the photo.
He was walking alone in the forest. Suddenly, a disembodied voice whispered his name.
I woke up to a strange noise. When I opened my eyes, a shadowy figure was standing at the foot of my bed.
One. 'I heard a knock on the door. It was my own reflection.'
I woke up in the middle of the night. There was a figure standing at the foot of my bed.