I've never really had nightmares, but the ones I had when I was little (killer waffles, don't ask) are hard to remember.
My most recent one was about this graveyard-like place with all of these little trinkets and such. However, there was a rule to the store: you could buy any trinket on display, but you were not allowed to run while you left the store. Nobody but the owner knew where the trinkets came from, but they were the item that was closest to the person that 'died'. If you ran while leaving the store, you would 'die' and the item you loved most would appear on the shelf.
Well, one of my friends ran out of the store, and on the shelf appeared an SNES game cartridge. I bought it as well as an SNES, not knowing that the cartridge belonged to my friend, and took them home to play on them.
After hooking up the SNES, I started up the game, which led me on a twisted adventure... Guiding my friend.
I can't remember the rest, but there was a part that freaked me out... Must've been the stupid laser traps... :c
The whole atmosphere of the dream was what mainly scared me...