I have had vivid dreams, wherein I have no recollection of my waking life, and I actually have "memories" of life events that never occurred in waking life. These dreams, when I have had them, often leave me in a very confused state when I wake, as I attempt to reconcile the "dream memories" with my memories of actual events that have taken place in waking life. I am also struck by how, within the dream a lifetime can pass by in the span of only a minute or so of REM activity in the "real world".
Now, to tie this in with the discussion on the book: I listened to an hour long conversation with Dr. Alexander on YouTube (for skeptiko.com), and even when asked directly, he could not provide any proof, or evidence, that this NDE he is documenting actually took place during the time in which he was in the coma. By his own admission, he states that he does not understand how it is even possible to remember any events that might have taken place during that time (i.e., new memories could not have been committed). Does it not stand to reason, that knowing that time can have little meaning in a dream state, even in the most realistic (or "hyper-realistic") dreams, that this all could have happened during a set of neurological events before or after the actual coma?
Being a materialist myself, I actually hold the premise of the dream-state to be the closest I can conceive of, or hope for, as an afterlife. I hope that those moments right before brain death are filled with lifetimes of events, rekindled memories of loved ones and pure bliss, so that I may fade into oblivion none-the-wiser that the lights were about to go out--that those moments might feel like forever in the instant before true death. I think that it is entirely plausible that this might have been exactly what the doctor experienced, but that he had the good fortune to come out of it. I also know that memories are malleable, and the time he spent attempting to recall what had occurred could have reshaped the original memory. (There are actually plenty of examples of this occurring all the time, with no intention of deception. This is one reason why eye-witness testimony is not given as much weight in court as many would think.)
So, admittedly I have not read the book (it is not out yet) but if the good doctor's interview on YouTube is any indication, there is no "proof" here, only wishful thinking and false hope for those that can't fathom an existence without a hereafter.