Explaining ____ (Ideas for WP2)

There have been many cases of people being awake during surgery after even after anesthesia. This could occur because maybe one's body does not respond to the anesthesia. They still fall asleep but they're awake. Meaning that their eyes are closed but they're mentally awake. They're paralyzed and cant move their eyes, any part of their body, or even yell. Just what the anesthesia is supposed to do. Except they're mind is awake and aware of everything happening. The patient is able to hear everything being said and the patient is also able to feel everything being done. For example. if the patient is having open heart surgery, they could feel the doctor cutting their chest open. The doctors don't know that the person is feeling pain because the patient cannot respond to the pain. The patient lies there feeling every pull and tug, every cut being made. I saw a movie called Awake where this happened and it interested me. How is it that this only happens to a number of people and how does one know that they wont feel pain after anesthesia? I have been intrigued by this for a while. Is it perhaps something in the anesthesia or something with the way our bodies work? Could there be tests done prior to surgery to make sure this won't happen to the patient? How common is this and how often does this happen? It's just crazy to me that someone could be fully aware of everything happening and the doctors don't know a thing. They will continue performing surgery because they think the patient cant feel a thing and that their body responded to the anesthesia.