I don't think we can truly answer this until we're put in that situation, but I think that dying people know their end is coming, even those who are healthy. One particular example was when I was 20, I was visiting my grandfather with my parents, and he went into the bathroom. After a few minutes, he came to us, and told his son (my father) to shave him, because God called for him, and he must go. So my dad shaved him, and my grandfather got into his bed, and he passed away after a few seconds. He died of old age, and he went away with a smile on his face. It was a really, really weird experience for me, and I have been thinking about it every now and then.