The book describes a near-death experience Alexander had while suffering from what should have been a fatal case of acute, gram-negative Escherichia coli bacterial meningitis, while on a ventilator and in a near death coma for one full week, with death eminently predicted by his medical experts - Alexander describes how the experience changed his perceptions of life and the afterlife.

In the fall of 2008, Alexander, a doctor at Lynchburg General Hospital in Virginia, contracted a very rare bacterial meningitis and spent seven days in a coma.

During this state, Alexander's experiences gave him reason to believe in consciousness after documented neocortex brain death.

[10][11] In a statement responding to the criticism, Alexander maintained that his representation of the experience was truthful and that he believed in the message contained in his book.

[11] Proof of Heaven was also criticized by scientists, including by neuroscientist Sam Harris, who described Alexander's NDE account on his blog as "alarmingly unscientific", and that claims of experiencing visions while his cerebral cortex was shut down demonstrated a failure to acknowledge existing brain science.