There is a phenomena that is quite common, and you may have even experienced this yourself. Where you see a black dog or a dark cat (or anything really) out of the corner of your eye. But when you turn to look at it full on, it's gone. And you know you're not mad. You really saw something move. It was what made you look that way in the first place.
There is a name for this phenomena (but I don't remember it). And a lot of people have it. So don't think you're alone or going crazy.
Now what it is, depends on which so called expert you talk to. I've been told that your peripheral vision is VERY sensitive, and that I am catching glimpses of other dimensions or realms. Okay. Whatever. I don't know what it is, but (like you) the thing that is sitting outside my room at the moment looking at me (I think it's a cat, judging by the flicking tail), isn't going to hurt me. It's just curious. And sure enough, I just turned my head to the left, and there's nothing there!
Is it another dimension? Or maybe my brain playing tricks on me? I don't know. But if you don't sense this thing means you harm, then it means you no harm.
But if you are getting freaked out by it and want to be rid of it, then I suggest smudging. I find smudging works a treat. Now whether you use a traditional sage smudge, or just a couple of incense sticks is entirely up to you. Both are just as effective in my experience. Merely waft the smoke in the area where it pops up, and tell it to go away. How you tell it to go away is entirely up to you. It can be a passage from a religious text (ie begone being of darkness) or something as simple as "I don't want to see you anymore". Just repeat the smudging and the affirmation every time it pops up. Eventually, they do get the hint and go away. It may happen the first time you try, it may take a week or so. But they do go away (personal experience).
Damn... that cat's back!
Good luck
