I used to suffer from night terrors through my teenage years and into my twenties. When I was younger, it was demons coming into my bedroom to attack me. The feelings of evil and terror were so vivid and real, I couldn't tell that it was only a dream. I'd be completely paralyzed - I couldn't speak or even whisper. I'd start praying in my head, then after a while I could whisper, then after I whispered, I was able to speak and beg them to leave.
At some point in my teenage years, the demons turned into aliens. They were often abducting me and performing horrible experiments and vivisection on me under the glare of a single, brilliant light. I experienced the same sensation of paralysis and not being able to call out for help.
That lasted into my twenties until I had one last dream. Every detail stood out so clearly and the terror and sense of evil was there. I woke up in the morning feeling drained, exhausted and fearful until I walked out into my living room. And I noticed just one single detail in my living room that was different from the dream the night before. There was an item in the room in my dream that I had moved to a different room the night before in real life.
The terrors had always seemed so incredibly real, and the dreams were so vivid and detailed that I had always had trouble distinguishing them from reality. That morning, seeing that one detail that had been missing from my dream, I finally was able to see that it was all only a dream. I haven't suffered from the terrors as badly since them. I've had a few dreams with the lucidity and paralysis, but now I can talk myself down. I always know now, somewhere in my mind, that it's just a dream.