Years ago I did Camp America - working at a camp in the wilds of Nevada - it was fantastic BTW and I would recommend it to anyone. Anyway, I shared a large platform tent with the sailing instructors (I was the windsurfing instructor). One of them was German, although her English was excellent. She used to suffer from extremely loud nightmares in which someone appeared to be chasing her and she would be screaming - loud enough that people in buildings nearby could hear her. She would wake me up with it every night. It was so bad that the lifeguard moved out because she was so scared. The other sailing instructor needless to say slept through it every night. Anyway I digress, at the time I found it interesting that she would always be screaming in English. So she obviously didn't dream in her 1st language.