The vision behind this is night terrors or sleep paralysis. Also, there is a little inspiration from the 1990 film Ghost where those dark entities come from hell to drag you into darkness. Could you imagine thinking you're awake in this situation and can't move or fight for your life, it's gut-wrenching feeling for me. I think darkness is present in all of our lives. One does not exist without the other, it's all about the balance of darkness and light.