Never have in the past, or never had any recollection of doing so...

So I'm at a cousins house right now, and his room gets pitch black at night. You cannot see anything at all, not even your hand in front of your face. Anyway, I woke up, and I didn't realize that I was awake. I thought I was in some metal chamber, that was just sealed off, completely non-lucid. So I get off the bed, and simply just thought the room dropped off a few feet there for no reason. I thought there were people behind it walking away, like they forgot me, and that I was going to be trapped and run out of air. So I start to get very worried and make my way over to the door as fast I can (there was a faint light coming from the crack by the floor), and I start stumbling toward it, when my cousin on the floor calls out my name, and then I realized that I was in his room and actually awake, and breathed a huge sigh of relief.

First time something like this has happened to me, was it sleepwalking?