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
Which of the following statements is true about REM sleep? 
Select and explain. 
A. It forms 50% of total sleep duration, B. Sympathetic activity increases, C. Muscle tone is normal, D. dreams are not memorized
B: Sympathetic activity increases
Answer: B: Sympathetic activity increases 
Explanation: REM sleep :

It forms 20-25% of total sleep duration
Sympathetic activity increases
Dreams are well memorized
Generalised muscular atony, excpet extraocular muscle, muscles of Penis.