>> john geiger, exporer and author has been investigating this phenomenon for years. lays out his theory. >> the story is always similar. there's a sense of another being, a presence very vividly. there's never any fear or panic when this being appears. there's just a sense of calm, peace. >>. >> reporter: it happened to stephanie schaub. >> i'm about as religious as a piece of wood. >> reporter: while cave diving she suddenly lost her guide rope. in an instant, her life was on the line. >> i suddenly realized i was in trouble. i could hear my heart bouncing in my ears. and i just kind of sat down on the floor and started crying. i never cried under water before. >> reporter: only weeks before stephanie's husband had died in a diving accident in the red sea. and now alone, she's facing her own dark death. >> reporter: suddenly t >> suddenly the cave brightened up. >> reporter: the words of her husband -- believe you can, believe you can't. either way, you're right. >> i thought i saw was a white thread. my guide line is white. so i floated up and lo and behold it was

>> reporter: john geiger, an internationally known explorer and author, has been investigating this phenomenonears. >> the stories are similar. there's a sense of another being, a presence, very vividly, a sense that there's something good there. something that will help them. >> reporter: it happened to stephanie. >> it was a day that pretty much sent signals to me. >> reporter: while cave diving for a research project in the bahamas, she suddenly lost her guide rope. >> i realized i was in trouble. i knew my heart rate, i could hear it bouncing in my ears. >> reporter: only weeks before, her husband and diving partner, rob palmer, had died in a diving accident in the red sea. now alone, she's facing her own dark death. >> suddenly, the whole cave brightened up. >> reporter: and into that world floated the words of her husband. believe you can, believe you can't. either way, you're right. >> and then, i calmed down. i saw what i thought was a thread. he was there for me in a way. >> reporter: so how is stephanie's experience to be explained? isn't this just possibly an hallucination? >> i thi