I half woke up, and I thought there was someone in my room. For some reason, I thought it was my friend Pete, but then I looked over, and it wasn't- it was kind of a big lumbering dude, and I only say "dude" because he/she was big and lumbering; I couldn't really make out a face. I couldn't do anything. Then said person kinda laid across my chest sideways. This was a little inconvenient. I could still kinda breathe, but maybe a little less. I couldn't do much. I felt like I could see everything fine, except the person; it was like he had a perception filter or something. I could move my hands, except to get the person off me, and I could talk but not to the person.
Eventually he got up and stood in the corner of the room. Same thing: I couldn't see him or talk to him, although I felt awake. At this point it was really just kind of annoying. I was thinking "well, what if I roll out of bed, maybe hitting the ground would wake me up for real." Luckily, before I could, I was awakened by a text message.
This has happened to me I think once before, and I don't think it's unusual for most people to get it a couple times. I bet if you didn't know about it, it'd be terrifying. Because you do, hopefully it'll be only a little bit scary, probably kind of annoying, and more interesting.
(side note: I guess this qualifies as lucid dream #3. But "I know I'm having sleep paralysis" is a lot less fun than "I know I'm dreaming!")