The more you expect it to happen the more it will. You want to start preparing yourself for it, do a bit of rehersal before you go to sleep. Maybe write a short story with you meeting the demon with a happy ending, or draw a few pictures of it and see if you can work out where it came from in your mind.

Maybe you can see it another way, you've got a dream sign right there! Maybe your sleeping mind is being nice to you and realized the best way to get you lucid is to use something shocking to get your attention.

There's always a silver lining, just be optimistic about it. You never know, that grim reaper may have loads of interesting things to tell you and things to teach you. Maybe your mind is wanting to teach you not to judge things on how they look.