I used to have wake-up-screaming nightmares several times a week. My husband got quite annoyed, because I was constantly waking him up with my screaming. Most of the time, my vocal cords were paralyzed from sleep, so I would make this screaming sound in my throat, which almost sounded more like a moan, except I'd make the sound as loud as possible, over and over, until I woke up. Sometimes the noise would wake me, but if it didn't, my hubby would wake me. On rare occasions, my vocal cords would not be paralyzed, so I'd scream full-force, which scared the crap out of my poor husband.
I used to have sleep paralysis, where I would wake up, but my brain would still be in sleep/REM mode, so I couldn't move. My eyes were open, but I was completely paralyzed. And because my brain thought I was still dreaming, I would hallucinate. Usually, I'd see a dark, shadowy figure standing in the doorway of my bedroom, which terrified me! Or I'd hear footsteps approaching, but couldn't see anyone. I would try to scream, but couldn't make more than a few whimpering sounds. Eventually, my brain would figure out that I was awake and the spell would break.
I used to have a lot of teeth-falling-out nightmares, too. (Probably because I'm terrified of the dentist and put off going for several years. Not the best decision I ever made. . . .) So, one time, in real life, I had a filling fall out and the tooth was too weak without the filling, so a good portion of the tooth broke off. It was my worst nightmare come to life, which meant I could no longer tell dream from reality while dreaming. Then, one day I realized that, in my dreams, when a tooth falls out, there's always a new tooth growing in underneath it. Just like when you lose a tooth as a kid. So I told myself, if a tooth falls out and there's a new tooth underneath, it means it's only a dream. This worked one time. I realized it was just a dream and all my anxiety disappeared. After that, it was like my subconscious figured out I wasn't scared of these dreams anymore, so it circumvented the only way I knew how to tell it was a dream, altering the dreams' parameters. Now, when my teeth fall out in a dream, there's no new tooth growing underneath it, so I can't tell if it's real or a dream. Which is horribly creepy, because it means my subconscious actually knows how to manipulate my dreams--and it's doing it to terrify me.
I suspect a good portion of my nightmares were caused by unresolved childhood trauma, because they mostly disappeared once I started coming to terms with things. It's also possible my bipolar medication is helping reduce the nightmares, too. These days, I only have a wake-up-screaming nightmare once every month or two, and I haven't had a sleep paralysis incident in several years. I do still have the teeth-falling-out nightmares occasionally, and I have another recurring nightmare where I'm chewing a huge wad of gum and I'll spit it out, but no matter how much gum I pull from my mouth, there's always more. It makes me gag just thinking about it.
It's weird, but I still remember the first nightmare I had, when I was maybe four years old. It was like a scary sci-fi story, with a plot and everything. Someday, I might turn it into a story. Even today, I have very vivid, detailed dreams with plots and sub-plots, characters, etc. In fact, most of the novels I've written were inspired by vivid dreams.
I've had some pretty intense nightmares over the years, ones where my husband gets shot in the head, for example, but the worst I ever had was a few months ago. In the dream, I somehow forgot about my cat. He was locked in a room without food or water for months, because I forgot about him. When I finally remembered, I hurried into the room to feed him. He came out to greet me, and he was literally a skeleton with skin. No fur, no muscle, no fat. Just skin and bones. It was absolutely horrifying! I knew that even if I fed him, there was no way he could survive. And it was made a thousand times worse by the fact that it was MY FAULT. I woke up crying, and even though it happened months ago, this dream still haunts me.