Family Differences in Trauma ?

My sister and I are Irish twins. We had virtually the exact same childhood, the only real difference between us is our personalities.

I have trauma nightmares nearly every night, and I found out a few days ago my sister doesn’t get trauma nightmares for some reason I’m reeling from this.

She has pretty much the same diagnosis I do, but seems like her general symptoms are significantly less severe than mine. I’m wondering why ?