I usually only remember my dreams if I actually get a decent sleep.
There was one strange exception. I was asleep in my car between classes when I went to my previous university and I had an extremely vivid dream of a war-like scenario. Picture an environment like, say, Gears of War.
I was only asleep for about an hour yet it was probably the most real dream I've ever had. It was raining and I could clearly feel the cold rain on my face. I ended up getting hurt in the dream (shot in the leg, I do believe) and I actually had an odd, lingering pain in my leg after I woke up.