Things that go bump in the night. Slithering or flailing people doing extraordinary things or knowing things that couldn't be known by natural means. Houses inhabited by demons that cause cabinets to open or things to fall off the walls. Have you experienced any of these kind of things? Not surprisingly many people would say yes. 

Do demons exist? Are they fallen angels? Evil spirits? Do people in seances hear their dead mother speaking or is it just demons?

If demons are real, then where do they come from? There is actually no origin story to demons as they are never called fallen angels in the Bible.