The Motel Room Bed and the "Incubus"

Lord, I almost forgot about this one, and how could I? This was the one of the scariest things that ever happened to me and that I think could ever happen to anybody.

I was living in a motel room at the time, several years ago, and not finding anything more suitable to live in I was quite content. Until one night...

As usual, I had turned off all the lights for a night's sleep. In the middle of the night I was suffocating while sleeping on my back. I awoke to the definite feeling that something had sat itself upon my face and physically blocked my airways. I fought to get up and struggled to turn on the light. There was no sign of anyone else in my room, but it was clear to me that something or someone had put itself on my face in my sleep. I got up and checked the entire room. The room was empty. The bathroom was empty. The single window and door were locked and bolted from inside. There was nothing under the bed. I checked everything in that room.

Satisfied that I was quite alone, I turned off all the lights again and returned to my bed. I managed to get back to sleep. Sometime during my slumber I had the same experience. Fighting for my breath I managed to get the invisible, suffocating thing off of me and struggled for the light switch again. I managed to turn the lights on again and repeated my inspection of my entire room and environment again. Nothing. And there were no signs that anybody nor anything else had been in the room with me.

I began to turn off the lights again, but left the bathroom lights on and the door open as a sort of a full-room nightlight. I managed to get back to sleep that night (I can't remember why I managed to continue to return to my sleep) and was not awoken again until it was time. My invisible visitor had failed to return, it seemed.

So what was it? Was it the legendary, mythical Incubus of the old tales? Or was it something else? Or was it purely my imagination? And, why did it happen to me twice in one night?