my son did the same thing!
it worried me, because my SO and i don't argue infront of him, and as far as i know he's never seen anything that would cause a nightmare. but i asked his dr. and she said its true. she said for one, birth was traumatizing! (if they remember it..?) but i did some more looking into it and read that when something scares a baby, like a loud noise or a mean face, they can actually remember that in their dreams!
at 12:04 AM on Nov. 13, 2009