When a person is dying why do they?

My father is dying from the MRSA Staph infection which has also caused pnuemonia. He has been in the hospital for 3 weeks and was declared terminal this past Friday. The doctor gave him 1 to 2 day but he has held on. His liver and kidneys have shut down, he has not eaten in 5 days and only takes 2 to 3 sips of his drink about twice a day. He has been very weak and completely out of it and as of yesterday they said he could pass any time. Today he was awake and talking, asking me questions. He doesn't even remember any one coming to visit him before today. How can he be so lucid after being so near death? Is this something that happens right before they die? He has a living will stating no nutrition or hydration and so forth. The doctors all say this is a normal process. I guess I am looking for reassurance that it is the normal process of the body shutting down.