I have not had any of these encounters! It is believed that you can be attacked by spirits if you believe in them. That is supposed to leave an open gateway to your head and life.
I have had two encounters however, with people who have had these types of experiences.
One, was a girl that I met and started dating. She wasn't the least bit crazy, and had no history of mental junk. She claimed that it all started for her when she let a friend stay with her. This friend of hers was into ouija boards and seances. The kid was paranoid and believed that he was being tormented by demons. She claimed that weird stuff was happening while he was there, but the worst happened, after he had left. She would wake up to find her outside dog, barricaded in her shed every morning. Plus the cinder block was pushed against it, holding the door shut, from the outside. At one point she claimed that she actually came face to face with this demon, she described it as having beady little eyes, and looked like an animal, with it's ears on top of its head. Only it walked upright like a human. It took her months and exorcisms on her home, before she got rid of the problems.
The other girl that I met, she was normal as well. There is an abandon mental hospital near me that closed down a long time ago. Her sister was in this hospital. She told me stories of that place and of her sister, that made neck hairs stand! I can't put the graphic details in here, but her sister ended up carving her roommate to pieces. Saying, "he" (referring to the demon who talked to her) "told me to do it, and now he is satisfied."
I googled the sister's name, and it all checked out. The scariest part was when she told me that before her sister went to the home, at four years old, she would sit in the corner of her room, speaking words that are not of our language, and clawing her arms and legs to blood.
I don't believe in what I've never seen, but I can't help but believe these girls.