I've had the dreaming thing before it happened - it's spooky but also awesome.
Anyway, as usual xkcd captures the bonker dream sensation well :
edit: here's the link http://xkcd.com/430/
Personally, the most disturbing one I had twice in a short spell, was going into a dark stairwell, responding to a noise, investigating, I can sense something bad is going to happen, and as I look back and forth down a pitch black corridor, I go to turn around and feel/hear the sound of a bullet hitting me in the temple. I feel an unstable sensation, aware that I'm about to die, but time appears to have slowed right down. I am overcome by a very warm sensation, possibly the blood flowing out of my head, and then just as I feel I'm about to go somewhere I wake up. Both times my hear rate was racing, I mean seriously, sweating all over and as I got out of bed to wander round I could barely walk. Fortunately just happened the twice but really felt like I understood that split-second sensation of death approaching. I was calm in the dream as it unfurled in slo-mo, but yeah.
So anyway...