So, I was on vacation last week and constantly on a tour bus driving around Europe. I spent most of the time on this bus drifting in and out of sleep but one particular time something happened that really freaked me out.
I woke up in my seat, opened my eyes, lifted my head, but suddenly, I felt my head fall back and I was completely unable to control it. I then noticed that I was entirely unable to move any part of my body. I tried to move my head, my feet, my arms, but I couldn't. I tried to catch the attention of my friend sitting next to me, because I could tell I had a frightened look on my face with my eyes wide open and my head flopped over like I were dead or something, but he was asleep. After trying really hard for about a minute, I was able to move my head just an inch which seemed to sort of shake off whatever was happening to me and I could move again. I woke up my friend to tell him what happened but he thought I was just dreaming the whole thing. How could it have been a dream when my eyes were open the whole time?

Can anyone explain what this was?