Question: Why do some people have negative NDEs?
Answer: Fear. It is fear that causes negative spiritual experiences. Fear also causes negative physical experiences.
I have been reading NDEs for over 18 years. While I hear that many are negative, I have actually found and read only a handful of negative experiences. I estimate that less than 3% of the experiences are negative.
If you rate the experiences from "mildly negative" to "wildly negative" you will usually find they start with being in the dark, alone and go on to seeing entities who try to hurt the experiencer.
The two elements that seem to "set up" the negative NDE are poor self-esteem and the belief in whatever monsters are seen. I have noticed that those reporting demons and devils were raised in fundamental religious organizations and hold an intense fear of going to hell. They have become focused on all the negative elements of their religious beliefs and expect to deal with them when they die. Their self-confidence has been eroded by the teachings of their religion to such a point that they also have trouble living in the physical world.
No matter what the monsters are: ghouls, vampires, ogres, demons, devils, etc. the experiencer must have been taught to fear these in physical life. Some organizations (very unfortunately) teach their members to fear God. Then confuse them further, by saying the devil can act like God when he wants. This teaching leaves the individual with no logical foundation to assess the events of life. They become fearful of all teachings except the ones of their particular religion or organization, and, in some cases, even God becomes the monster who wants to hurt them.
The main thought here is to address our fearful thoughts and exchange them for thoughts of love. It really doesn't matter what form the fear takes, it is the fear itself that keeps us from enjoying a happy, loving life. There is really nothing for us to fear, not even fear itself, once we discover who we are and why we are here.
Emmanuel, a spirit guide, was speaking to a group of people about challenging and "walking-through" their fear when a voice from the back of the room shouted: "Emmanuel, would you walk through the gates of hell?" The reply from Emmanuel was: "with a smile on my face." Don't put up with fear, walk through the gates of your hell into the Loving Light of God.
There is a more detailed discussion of why people see different things in FAQ number 3.