Force?

This happened a few years back, I don't know what to call it but this is the first time I've actually felt something.

I was in Graphics class, we were sketching things to learn the basic skill of Graphic drawing. The classes desks were in rows of two, on each side of the classroom with a big walkway through the middle and small walkways between the rows. My friend was sitting beside me, and we were talking to someone behind us but no one was sitting in front.

The tables lean up and I had stretched my arms out on it, with my hands hanging over the side. In one hand I held a pencil, pointing straight out in front of me.

So my friends and I were talking away, in our little group when something walked into my pencil, causing it to move where the person was going as if someone identically walked into it. Seeing as I thought it was a real person as the force of it was very strong, I turned my head around to say sorry. As I was about to say it, nothing was there.

I looked around the room, thinking it was someone and they were just sitting down but everyone had already sat down. By the time they touched my pencil and by the time I looked, I would have seen them sit down or something but there was no one.

The way in which the pencil moved with the force was in the direction to the wall, as my desk was right beside it. So for it to be a person, they would've noticed it and it would have gone the opposite direction when they walked back.

I had been told my hand got cramp or I was just imagining things, but my hand never got cramp, it was perfectly fine and the force hit my pencil not my hand. Seeing as I was in conversation and not thinking about ghosts etc, I doubt it's my imagination as I saw nothing.

I'm still confused to this day what it could have been but I am certain it was something. It's not a big experience, but it is definitely something.