Near Death Experiences

Do near death experiences really exist? Or are they just figments of our imaginations? There is no strong evidence to support this claim, as stated in our book, and maybe there are simpler explanations as to why we feel as if we have had NDEs. There a tons of stories from people who have said they had a near death experience, even my sister thinks she experienced one. Last year she had to have surgery to remove her cancerous thyroid, and due to complications with the removal, she had to undergo another surgery. During that second surgery, my sister believes she "died" because she was in a white room and said she saw my grandma, who passed away 2 years ago. She has vivid details and has described her experience to us multiple times. Could she really have had a near death experience?
In our Psychology text book it states that alternative explanations for NDEs could be based on the changes in the chemistry of the brain associated with cardiac arrest, anesthesia, and other physical traumas. Our brains could just be releasing different chemicals and neurotransmitters that make us believe that we are experiencing bright lights or seeing things/ people that we couldn't possibly truly be witnessing. People could think they are experiencing NDEs because of certain psychedelic drugs they are taking as well. There is no significant amount of evidence that can prove that NDEs are a real thing yet. Many scientists say that the characteristics of near death experiences could just be the effects of an oxygen deprived brain.

I found some of the information on this site interesting. It talks about interesting stories of near death experiences and tries to show the evidence that they are real.

http://readersupportednews.org/pm-section/398-science/7170-new-evidence-suggests-that-the-near-death-experience-is-the-spirit-leaving-the-body-and-not-just-a-dying-brain