A Dark Thing, Wish I Knew What It Was

This is kind of old, but I've never come to a satisfactory conclusion on what it was, and I'd like some help in figuring it out and making sure it can never come back to me again.

I was fairly young, maybe eleven when it first came, and it terrified me. I had until then always slept easily, but insomnia laid its curse upon me at that time in my life, and it came with it. I would wake suddenly, shivering under my blankets no matter how warm the room was, and it would be there, looking down at me. It was always in the same corner of the room, no matter where I put the bed, and always somehow crouched up in the corner where the ceiling met the walls. It was a scrawny, long limbed thing, humanoid in shape, but with arms and legs far too thin that ended in long bony fingerlike appendages with clawed tips on both sets of limbs. It had no identifying changes in color, and a round, featureless head, but I could always feel it looking at me, however it did so.

My sleep got worse, but it didn't increase the frequency of my seeing it, maybe once a week or so. I wasn't fond of horror movies or books, nor did it come on specific nights that I might be able to say 'Man, I gotta lay off the tacos, they give me weird nightmares.' And I wasn't asleep, I know the difference in feeling between the 'almost awake but dreaming' state and the 'awake' state. Then I began to feel it stalking me in the daytime, somehow. It was never visible then, but I felt it whenever I went up or down the staircase to my room, causing me to rush in either direction to keep it away. It never came at night when someone was there with me for a sleepover, nor did it stalk me in the day if I had a friend over to go up the stairs with me. Most of my pets didn't react in the room, but they made no effort to go up to it either, and the pet fish I would occasionally have would go belly up relatively fast, and I didn't overfeed them or starve them, and kept their water nice and fresh.

The Thing, as I came to think of it, continued to come for about two years, sometimes with longer breaks in its appearances, until my Grandfather died when I was about thirteen. Six months after that, I woke to see The Thing cowering back in its corner as best it could, with a large, vaguely luminous figure holding a baseball shaped bat in its hands standing next to my bed. My Grandfather had been talented at baseball until he took shrapnel in the arm during WWII, and I remain convinced to this day that he put The Thing in its place about me. A week later, my Dad was bringing my brother home from school and looked up to see my Grandfather sitting on the porch, and my Mom, who believes more in things that are not of this particular plane then my Dad, went through the house with ceremonially blessed sage and a cleansing prayer, and after that The Thing did not show itself again.

As I've said, The Thing hasn't been back since then, but lately I feel nervous, and would like to know what it might have been and if there are ways to make sure its spindly form doesn't take up residence in my life once again, so any help would be great.