Here's how it happens.

You're drifting off to sleep; or maybe you wake up in the middle of the night. You feel a presence in the room.

You see something out of the corner of your eye. You try to look but you can't move. You try to call out, but you're unable to make a sound. There's an invisible weight on your chest. Even breathing is difficult.

You strain to look and then you see it. The shadow of a person. You can't detect any features but every instinct you have tells you: this is entity is not friendly.

You hear a light hum, maybe a rush of air and the dark entity vanishes.

You've just encountered a shadow person. 

This one was pretty benign, but there are some shadow people sightings that are more intense. More real. These encounters can be traumatic and in some cases: violent.

I should know. Because it happened to me.