I remember getting wisdom teeth extracted, and it was as if I just didn't exist. I have never had such a null feeling. I don't know if you can really tell if you are sleeping, but it isn't the same as dead. And even when under, I somehow was guided to my feet to a waiting room to wake up--even though I don't remember it.
There have been times where I felt as if I were going to sleep too fast, and would wake up, and drift to sleep more slowly.