Early Morning Bed Vibrations

Before I do any posting, I would like to clarify one thing: I am not sure at all if this was a ghost or not, because while I have experienced various hauntings personally, I still can never be sure. But still, this seems... Shall we say, appropriately paranormal.

It was this morning, and I woke with a start at the tap of my roommate, telling me that my alarm was going off. See, I have this weird alarm clock that can have a vibrating disc attached to it to provide, shall we say, that extra dose of chaos to jolt you awake when the pterodactyl shriek from the clock itself doesn't do the trick and had showed this to my roommate while I was moving in. I didn't attach it though, when I set the clock up that night. Bit of overkill.

I actually hadn't even turned on the alarm itself, and the disc was in a drawer about two feet below the bed. Even though my phone had the alarm set (just noise), it was more than an hour before it was supposed to go off. My alarm wasn't going off, so I went back to sleep.

My bed (mostly mattress), according to his testimony when I woke up that morning, had randomly started vibrating powerfully in one solid pulse, shaking me with it, unbeknownst to me. Just my bed, mind you. He had thought it was the vibrating disc. That disc wasn't connected to the clock, which wasn't even set for an alarm.

I hadn't moved the bed, he told me, and I was just along for the ride. There was nothing else in the room that could have done it. With no explanation for this event, I'm left to wonder what actually was going on. I'm stumped.

Any thoughts?