Nightmares

Ok..so basically Danner has been having nightmares. It has been happening almost every night and it happens around the same time every night. About an hour or so after she falls asleep she wakes up crying. When I go in there she is usually standing up or sitting up. Her eyes are closed still and she mumbles something. Some nights I can make out what she says but most nights I can't. Tonight it was something about Sawyer hurting her. The solution is pretty easy......lie her back down and tuck her back in. She doesnt even wake up. She quiets back down and sleeps peacefully the rest of the night. Weird, right? I wonder what could be causing this? Anyone have any suggestions?