Is it possible that some people can't get a regular sleep paralysis, for example sleepwalkers?
I'm asking this because I was laying in my bed for an hour or so, I thought that I finally achieved SP, but to my disappointment I could still move. I counted my breaths for a while, up to 100 and then I started over. When I got the part when the hypnagogic imagery kicked in I just relaxed and observed the shapes, then as I was starting to see dreamlike sceneries my body, which already felt really heavy, like something was squashing me into the mattress, started to vibrate from head to toe, it was really intense. As the vibrations wore of I decided that I'll open my eyes, I was curious from reading other people's SP experiences, but all I could see was my regular bedroom and I could easily move too.
So what was this? If not SP, was I at least getting close?