A few weeks ago I saw a shadow in the corner of my eye. I was in my kitchen with the door closed listening to music, it was late, like 1 in the morning, I went by the door and saw something black, it looked like smoke and it was wearing like a white mask. When I looked through the door's window it was nothing there. In the next day I was in my room when I saw it again, in the other room, peeking from the corner, again, it vanished when I checked. I see it almost every night peeking at me. It's been almost a month now, what can I do?