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?
explain NDEs. Neuroscience research suggests that an NDE is a subjective phenomenon resulting from "disturbed bodily multisensory integration" that occurs during life-threatening events.
Etymology.
The equivalent French term "expérience de mort imminente" (experience of imminent death) was proposed by the French psychologist and epistemologist Victor Egger as a result of discussions in the 1890s among philosophers and psychologists concerning climbers' stories of the panoramic life review during falls. In 1892 a series of subjective observations by workers falling from scaffolds, war soldiers who suffered
Near-death experience
A near-death experience (NDE) is a personal experience associated with death or impending death. When positive, such experiences may encompass a variety of sensations including detachment from the body, feelings of levitation, total serenity, security, warmth, the experience of absolute dissolution, and the presence of a light. When negative, such experiences may include sensations of torment and torture. NDEs are a recognized part of some transcendental and religious beliefs in an afterlife.
Different models have been described to