Barry knew Alice was tired, but he was surprised that the argument between their three-year-old twin boys did not awaken her.She had not been asleep very long and occasionally changed her position, but did not wake.Alice is probably in

Answer 1

I searched Google under the key words "sleep stages & environmental awareness" to get this source:

http://www.healthyplace.com/other-info/sleep-disorders/sleep-basics-why-we-sleep-and-how-sleeping-works/

"Stage N2 sleep is characterized by a complete loss of environmental awareness and this stage occupies 45% - 55% of adult sleep."

In the future, you can find the information you desire more quickly, if you use appropriate key words to do your own search. Also see http://hanlib.sou.edu/searchtools/.