I'd have to say they are a spiritual experience, a temporary lifting of the veil that hides the spirit world.
MANY near death experience reports come from people who have no medical or life-threatening condition. You don't have to be near death to have a near-death experience. These are tremendously powerful spiritually transformative events. Read them at www.nderf.org. then click on "Current NDEs" - - it'll blow your mind!