How do people hear when asleep?

Well, when people are asleep, their minds go into a state of REM (rapid eye movement), and they are not really "unconscious", their brains are always working. So in their sub-conscious, they still hear people. Unless you are a heavy sleeper.. It will be hard to awake from REM. But once I was asleep on my couch and my sister was throwing up in the bathroom, and I was asleep. She was yelling and yelling at me, and when I was dreaming, I heard her voice, and woke up. It was pretty weird..

But I'm glad I could help!