You ask yourself, how can you be living but dead? It is not possible. Yet it can be and it can be slightly reversible, but realistically, for most people, it is not. Living but dead, is walking in the world of the in-between. Standing with one foot on the terra firma and the other foot in the air above it.
Death is an odd configuration of simple reality. You stop breathing, they say you stop being. It is possible to believe it is more than that. It is possible to say that you do stop breathing but you are not actually nonexistent. You are on another plane of existence. You do, in some fact, exist, that is a belief of many. It is real according to many, the ones who see and hear those on that plane, namely, mediums.
A fatally ill person usually begins to realize on some level that they are moving toward death. They might still have hope, which can be encouraged, but tinged with that hope is a bit of reality. Hope can bring a lot of positive energy to a situation. Positive changes can happen. This is truly a transitioning time for anyone in it. How do you prepare someone, even yourself for the situation that looms?
I have found that talking and sharing with the person helps them focus on other things, other times. Helping them wade through personal belongings, deciding what to throw out, who to give something too is very helpful if the person is willing to do that. Denial is a powerful thing and sometimes people in that place cannot bear to part with material things.
Moving someone from the denial, closer to what reality might be is a gift to the person. It helps them prepare. Just as a woman who is pregnant might want to fix things and make them ready for an impending birth, an act which is usually called "nesting", a dying person can sometimes wish to do a similar thing. They might want to feel that they are prepared, have been methodical about their wealth and possessions, their debts and responsibilities. Often people create wills and find people to be their executor. For many this is a last act kind of experience, for many who are schooled in their own existence, they anticipate the need for such things long before such events transpire.
Many people shrink from the idea of death and what it can mean. They ignore it as if for some it does not exist. Some believe it is such a natural part of the cycle of life that they are able to share and experience things long before they are seemingly "adult" enough to do so. Through experience, this can be the better way. If as a young child you experience the death of a close family member, it is good not to be hidden from it. It is a positive thing to visit that person, perhaps to see part of their decline and to still communicate with them, as possible, sharing life, joy and laughter too. Why? This is a teachable moment that lasts a lifetime, this helps a person experience things on a level that they can then accept that this is a part of all life. There is, in some cultures and experiences, a desire to shield a child from anything that might be upsetting to them, but in the end, this only inflames the experience for some and robs others of emotional connection in others. If a child sees a relative in the process of illness and then learns that they have passed, they might be more willing to accept and understand that the deceased person will now be no longer suffering that illness.
They say that young people take chances, and experience life from the position that nothing is going to happen, that they have no fear, that they are eternal, in a way. This is a good thing and a bad thing. Life with carefree abandon is often a very fertile one, for ideas, experiences and well, just plain living. Life in fear of mortal consequence is not always conducive to idea, to experience or the color of life. In the end, when you are dangling with one foot in this world and one foot in the next, it is better to have had the experience of the fertile life, the one where you lived as your life would allow, pulling out the stops full on. That makes the time of transition memory filled and anticipatory of the great next adventure, as well it might be.