And they compared the patients who had NDEs with groups of others who didn't.

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"To our surprise, NDEs were much richer than any imagined event or any real event of these coma survivors, " Laureys reported.

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Scientific research on people having NDEs is tough, because the exact instant that they occur is unknown, making them nearly impossible to observe, Laureys said.

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They compared NDEs with other memories of intense real-life events like marriages and births, but also with memories of dreams and thoughts -- things that did not occur in physical reality.

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