Night of the living dead.... literally

I had a night, a few days ago, where I don't remember getting into bed. I remember that I was tired and heading to bed but I was so tired that the next thing I remember is waking in the middle of the night sleeping on the wrong pillow. I have a certain pillow I use as I'm sure everyone does and this pillow was not it! And I was mad about that but it was too much effort to get the right pillow so I just went back to sleep. When I woke the next morning I tried to remember the events of the previous night that led me to the wrong pillow. Nothing. I can't remember pulling back the covers, or what was on tv, or setting my alarm, even though.... thank goodness I did that.