In a wide-ranging investigation of Alexander's story and medical background, Esquire magazine reported (August 2013 issue) that prior to the publication of Proof of Heaven, Alexander had been terminated or suspended from multiple hospital positions, and had been the subject of several malpractice lawsuits, including at least two involving the alteration of medical records to cover up a medical error. The magazine also found what it claimed were discrepancies with regard to Alexander's version of events in the book. Among the discrepancies, according to an account of the Esquire article in Forbes, was that "Alexander writes that he slipped into the coma as a result of severe bacterial meningitis and had no higher brain activity, while a doctor who cared for him says the coma was medically induced and the patient was conscious, though hallucinating."
Alexander issued a statement after the Esquire article's publication: "I wrote a truthful account of my experiences in PROOF OF HEAVEN and have acknowledged in the book both my professional and personal accomplishments and my setbacks. I stand by every word in this book and have made its message the purpose of my life. Esquire's cynical article distorts the facts of my 25-year career as a neurosurgeon and is a textbook example of how unsupported assertions and cherry-picked information can be assembled at the expense of the truth."
Alexander’s book and publicity campaign have been criticized by scientists, including neuroscientist Sam Harris, who described Alexander’s NDE account (chronicled in Newsweek, October 2012) as “alarmingly unscientific,” and that “everything — absolutely everything — in Alexander’s account rests on repeated assertions that his visions of heaven occurred while his cerebral cortex was 'shut down,' 'inactivated,' 'completely shut down,' 'totally offline,' and 'stunned to complete inactivity.' The evidence he provides for this claim is not only inadequate — it suggests that he doesn’t know anything about the relevant brain science.” “Even in cases where the brain is alleged to have shut down, its activity must return if the subject is to survive and describe the experience. In such cases, there is generally no way to establish that the NDE occurred while the brain was offline.” Neurologist and writer Oliver Sacks agreed with Harris, saying that "to deny the possibility of any natural explanation for an NDE, as Dr. Alexander does, is more than unscientific — it is antiscientific."..."The one most plausible hypothesis in Dr. Alexander's case...is that his NDE occurred not during his coma, but as he was surfacing from the coma and his cortex was returning to full function. It is curious that he does not allow this obvious and natural explanation, but instead insists on a supernatural one."
In November 2012, Alexander responded to critics in a second Newsweek article: "My synapses—the spaces between the neurons of the brain that support the electrochemical activity that makes the brain function — were not simply compromised during my experience. They were stopped. Only isolated pockets of deep cortical neurons were still sputtering, but no broad networks capable of generating anything like what we call 'consciousness.' The E. coli bacteria that flooded my brain during my illness made sure of that. My doctors have told me that according to all the brain tests they were doing, there was no way that any of the functions including vision, hearing, emotion, memory, language, or logic could possibly have been intact."