The laying being

I haven't expirience that much of paranormal activities in my life. But when i was 13 in a random day, after several weeks after my grand father died. I decided to open the door of his bedroom, he died in a very sad way by an infection in his leg that never healed because he had diabetes.
When i went to his room, the door was already open. I stepped right out side of it to get a look but it was very dark, the light coming from outside barely touched the floor and some parts of the bed.
Something pulled my will and proced to walk inside of the room, i turned on the lights. But nothing was in there, i spended a few minutes in there till i get bored. But, when i was going out, i felt the springs of the bed making a noise. My head turned to look the bed and i saw him, a dark silhouette with white eyes looking right throught my soul. It was under the sheets with his head and i think was his arm hanging from the side of the bed.
I was freezed in there, and freaked out after i heard him moaning. I fell in to my butt and then run as fast as i could in silence until i found my mom. I told her what i saw, and she belived me (I think). So we went again to my grand father's bedroom to prove if my imagination was doing something weird. But when we arrived there, the bed of my grand dad was a mess, as if something or someone used it.
My mother said to me that it could be him, because he died in his bed. So i wasn't that afraid after that. Some time later he appeard in front of me in the corridor, moving to the main door and then he vanished right away. I think he finally left the hous,e because it was the last time that i felt his presence.