This story actually happened to my mom when she was a teenager; she was very reluctant to talk about it but I was too curious. When she was about 17-18 years old my mom was still in high school living in the town of Dobrich, Bulgaria. She was living alone with my uncle as my grandparents' jobs required them to spend most of their time in a nearby village.
Anyways, she told me that in the middle of the night she would wake up in her room for no apparent reason. As soon as she wakes a woman in a long white dress, with black hair would enter the room. My mom says she just stood in her bed frozen and unable to react.
They used to have a heater with a couple of noisy switches. What this woman would do is enter the room and start switching the heater on and off, on and off. She would just do this for a while and then leave. This was happening every night for a couple of months.
At some point my mom decided to tell my grandma as she was getting very tired, not being able to sleep properly. My grandma didn't believe her first. However, when my mom started getting continuous nose bleeds that wouldn't stop for hours, she got worried. My grandma decided to sleep in my mom's room for a couple of nights to see if what's going on. Again the woman in white would enter slowly doing the exact same thing. When my mom woke my grandma the woman disappeared. As my mom's health was getting worse they decided to call a priest to bless the flat. Nothing has happened since.
I honestly believe that there is something in that room that for some reason only my mom and I can sense. I was living in that flat as well for about 5 years, sleeping in the same room. It must have been between the ages of 3-8. I was so afraid of the night. I never saw anything as scary as that, but even from this early age I clearly remember that every single night I would have horrible nightmares where I would die in lots of different ways. This was so traumatizing that it is pretty much all I can remember from my time in that flat.
Furthermore, in my early childhood I was a very sickly kid for some reason. I had asthma and was sick and on antibiotics almost all the time. Once I moved out of the flat and to Sofia (the capital of Bulgaria) my health became much better and my asthma disappeared!