Sorry you had that bad nightmare. I get some really bad ones sometimes. It could be the PTSD.

I don't know why we remember the nightmares more than the good dreams.

I have a hypothesis but it is probably wrong. I suspect that the human brain is wired to remember bad things because they can sometimes pose risks to survival.

Maybe when human beings were living in caves thousands of years ago, it was important to remember which things were poisonous to eat, the sound of a snake slithering, the difference between the calls of a monkey and those of a panther and stuff like that.

We needed to remember not to stick our hands into a fire. Since we remember bad things in the day perhaps we also remember bad things that happened in the night. I'm probably wrong about that though.

Actually I don't know why. Just sorry that happened to you!