Trigger warning for child abuse

The question is in the thread title. When I was 6 years old, my mom had some sort of mental breakdown and excessively beat me and my younger sister, told us she wanted us to die, and repeatedly threatened to kill us. The incident was isolated and lasted only about 10 minutes or so, but the psychological effects of it lasted a very long time and never quite left me.

We had often went into her room at night and slept in her bed, and she was always fine with it. But one night, she just snapped, and made me and my sister take turns getting hit and thrown around on her bed. She was mostly throwing us, pushing us down, yanking our arms and twisting them, and taking heavy blows at our backs with her whole arm, sending us flying across the bed. It was enough to leave bruises, but we didn't have many since we were mostly landing on a soft bed. But to me, that makes it all the more sinister, because she was hurting us in a way to deliberately avoid leaving any evidence, by having us hit something soft. I remember distinctly when my sister hit her head really hard on the headboard and cried out in pain. But the most painful part of it was what my mom was saying as she was doing this. I remember the vile, hateful tone in her voice, and the wild look on her face. She kept saying, over and over, these phrases: "What am I gonna do with you" "I wish you were F-ing dead" "I want you to F-ing die" "I'm gonna F-ing kill you". The terror I felt was incredible. I didn't understand what was going on, and I thought my mom had turned into a monster or that I was being punished for something I didn't understand. I thought my mom was going to kill me and my sister. My dad eventually stopped it, but not after he stood in the adjoining bathroom of their master bedroom pretending he couldn't see what was happening. He was likely too scared to intervene at first, but it made me feel invisible and unimportant.

The next day she gave an apology, and said some other things that I don't remember. But it was never spoken about again, and any time I'd ask a question, like "mommy, what was wrong when you did that to me", she'd change the subject or get in a really bad mood and be snappy all day. So I stayed quiet about it, but I'm sure it twisted and warped my mind. I was only 6. I wondered: Why did my mom want to kill me / what did I do wrong / is there something wrong with me / does she still want to kill me / does she really love me / why didn't my dad help me sooner, why couldn't he see me

Right after the incident, I was so confused and hurt all the time but had no outlet and no one to talk to. My sister was too young to remember thankfully. But also too young to talk to, being only 3. I started having really violent fantasies and urges to hurt small animals. I hate admitting this, but I'm sure it's tied to what my mom did. Eventually the urges became so strong that I started torturing and killing lizards, and as I'd do it I'd say those same phrases that my mom would say to me. I knew that what I was doing was wrong, but I couldn't control the urges. I felt some sort of release when I did it, idk why. It wasn't too often, maybe once a month. This behavior stopped when I was about 9. I still feel intense guilt about it all the time. I'm not a psychopath, I'm very compassionate now, and I never feel any urge to kill people or animals, but I still sometimes indulge in violent revenge fantasies toward people who've hurt me. And sometimes they become so intense that I literally cannot think of or concentrate on anything else for the whole day or days. This might be due to my OCD though, idk.

The question is, can a single incident of physical and psychological abuse really damage a child that much? Or is there something seriously wrong with me? I'm 23 now, but my anxiety/depression is flaring up lately and I can't get this out of my head.

I've never told anyone about this. I just want my feelings to be validated in some way, even if it's just over the internet. I need to know I'm not just being oversensitive.