Worst and most vivid one I had was where an ex-girlfriend shot me in the throat with a shotgun. I could remember, and FEEL, spinning around and falling chest down. I remember seeing the ex sitting on the floor in front of me, white as a sheet from fright and spattered heavily with my blood. I remember trying to raise my head, but being unable to, because all the muscles were blasted away. I remember trying to say something, but only wet gurgling noises coming out. I remember dying, with everything fading to black, and then fading to something I can only describe as "beyond black", like a dark grayish mist. After God knows how much time, could've been between 2-3 seconds up to 30 seconds, I woke up, screaming and drenched in sweat so bad you'd have thought I just got out of the shower.
I remember actually feeling, a tactile feeling, every little thing that happened. The coldness of the granite floor, the slight wet warmth of my blood, even the pain of the shotgun blast, which was like a very painful stinging and ripping feeling. Every little detail was so sharp and vivid. That dream scared the hell out of me so badly I couldn't sleep for the next 3 nights. On the fourth night I only got 2 hours.