A near-death experience is a personal experience associated with death or impending death. Have you ever had one, hopefully not!
I have not, but that sounds very scary.
They say there can be a feeling of detachment from the body, levitation, total peace, security, and/or the presence of light. 
I cannot even imagine how that would feel. what causes this?
They believe being that close to death comes from disturbed bodily multisensory integration. Basically the sensors in us are on overload