My nightmares are often about my traumas, but the traumas often intersect or get jumbled in my dreams. For instance, I was sexually molested and assaulted when I was 3-and-a-half years-old (probably numerously, though I was so young that my memories of it are fragmented), was sexually molested by a doctor, was pretty brutally raped on two occasions when I was an adult, and was repeatedly sexually assaulted by someone whom I thought was a good friend.
My grandfather was very abusive towards me. Never physically or sexually - verbally and emotionally. His verbal and emotional abuse felt like physical abuse, though. My nightmares often feature me being sexually assaulted or raped by my grandfather. A couple of times, I've had nightmares about my mother doing that to me, too, and she also never sexually abused me. (She was sometimes physically abusive, though - hard smacks, slaps across the face, that kind of thing.)
I also have a lot of nightmares that feature discovering my mother is alive (she died of cancer 14 years ago) and my mother accusing me of abandoning her. Usually in the dream, my grandmother has hidden from me for all these years that my mother is alive, and usually joins in with accusing me of abandoning Mum, even though she was the one who hid it from me in the dream. It's always extremely distressing and I have woken up crying from those dreams.
My brain jumbles a lot of my trauma together into really bad nightmares that leave me confused, disoriented and afraid when I wake up.
That said, I also have a lot of nightmares that don't seem to involve any of my traumas as a catalyst. But in almost all of my nightmares, horrible things are happening to me that cause me to feel utterly out of control and violated. So, I guess my brain is also trying to process the way my traumas have manifested in me, too.