Demonic Dream Interpretation?

I keep having this recurring nightmare. A black demon figure, very tall and jet black. So black you can't make out its features. It's shaped like if you sketch on paper sharp, brutal lines using a black ink pen. It disguises itself as a black cat. In the past if I dreamt demons, I would fight them, but this one, I just get super scared. I would be sleeping and my heart would be racing. It doesn't do anything to me, just follows me and I would see it through a window staring at me. An explanation would be greatly appreciated. Thank you