Life's failures. Dead friends & family. High school-but-I'm-my-current-age.
Sometimes it's interesting and even pseudo-enlightening/philosophical, but mostly it's depressing.
In my younger years, my nightmares were more like... Getting chased by a pack of dogs. A group of adult bears attacks. I fall in between the cracks of an escalator. Lawnmower tries to kill me. Those were all individual dreams, not the same one.