Ferthepoet:

Might I ask how old you are? What happened to you sounds like a "night terror" or "sleep terror." They are more common in children, but have been known to happen to a number of adults as well. They happen in non-REM sleep, however the images seen are just as convincing. There is no sleep-paralysis holding your body down during these occurances, and many people have actually injured themselves, severly, trying to escape the horrifying images that have seemed to transition from sleep to awakening. I once saw a news cast about a teenage girl with night terrors so bad, that her family has to secure all of the doors and windows in the house while she sleeps, and take turns keeping watch over her. Before they'd done this, during one of her night terror episodes, she got out of bed, ran to her patio door, trying to escape the images, and jumped off the second floor balcony. She was still "asleep," but so terrifyied that, even though she broke something when she hit the ground (forgot what it was) she got to her feet and ran into the woods screaming, where her folks found her, later. The only thing strange about your situation is that you didn't seem particularly terrified, and night terrors are usually balls-to-the-wall Horrifying, however I think it is a good chance that it was the same sort of event.