It's morning time right, I feel this pain on my arm as I get up and I see what looks to be a small pentagram carved into my left bicep. It is perfectly symmetrical like someone had a Stencil or something. Except my blood was the ink because a small thin line of blood marked the lines of the pentagram. I freaked out and had to wear a jacket for the entire day. I kept checking and it was there the entire day. Next night when I woke in the morning, the Pentagram was gone. I know what your thinking. Maybe I was hallucinating, but I dont know. Any explanations anyone?
If it was truly made by cutting the skin on your arm then it wouldn't have vanished overnight. So let's throw out the idea that it was cut into your skin.
More likely that it was simply coincidence and left by wrinkles in your sheet or by sleeping on something. Or you may have accidentally scratched yourself. And it is quite possible that you are reading more into the symbol you thought you saw than was actually there.
What if really unlikely is that this was caused by any entity being present and doodling on your body.