I didn't have nightmares until I started work as an aircraft repairman.

I used to dream about exploring places. I remember one where I was swimming through this large building, I could breathe underwater but it was underwater, and it was just "let's see what else is here."

Now I dream of inevitable threat. One I remember pretty vividly was being trapped in this cave, there was no way in or out of this 30x30 foot room, and in the middle of it stood a gallows dangling a noose over the head of a ...man? Who turned and started slowly stomping toward me, and the gallows shifted around to keep the noose over his head, making a repetitive clanking sound. Weird imagery on the typical "thing slowly chasing you" dream.