This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
[{'content': 'Nightmare is seen in : \nSelect and explain. \nA. REM sleep, B. Stage II NREM sleep, C. Stage IV NREM sleep, D. Stage I NREM sleep', 'role': 'user'}, {'content': 'Answer: A \nExplanation: A i.e. REM sleep', 'role': 'assistant'}]