Sometimes referred to as the final mystery, the truth behind what happens when we die is unclear.
Some people who've had near-death experiences describe seeing a bright light, while others said they heard voices or were able to look at their own dying bodies.
Whether these are evidence of an afterlife or the brain just doing what it needs to do in what it thinks are its final moments, we don't know.
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Two women who 'came back from the dead' have described what the afterlife they both saw is like, and one says it was so good that she wants to go back.
Jessie Sawyer and Betty J. Eadie had similar experiences of being dead and seeing what could be described as an afterlife in a series of surreal moments.
78-year-old Betty had a near-death experience after an operation when she felt 'this sensation of my spirit coming out of body at tremendous speed' and looked down to see her own body lying on a bed.
Thinking she was dead, she then said she saw a trio of 'really ancient men' who told her she had died, and then she flew her spirit out of the window to her house, where she saw her family and the lives they'd lead.
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She said she was then whisked back to her hospital bed and went into a tunnel where she met Jesus Christ, who she says 'hugged me' and told her 'it's not yet your time'.
Betty said three angels then appeared and took her to a beautiful garden before she met God in the form of 'the most beautiful man I've ever seen', who told her she had to go back to her body.
She said that five years after the incident she told her doctor all about it, who confirmed she had medically been dead for some time, and that she wants to go back to the afterlife she saw.
Betty would later go on to record her close brush with death and what happened afterwards in a book titled Embraced by the Light.
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As for Jessie, she said she 'died' aged 31 and that the experience has left her no longer fearing death.
She said she saw the figure of one of her best friends who had died two years ago along with a bright light, before falling back into her own body 'which hurt'.
Doctors told her they thought she had briefly died, and had been 'walking the line between life and death for a while'.
These accounts tally with many others from people who medically died or came close to death and came back from the brink.
Obviously near death experiences are something that are all but impossible to properly test, as the person would have to be in a life threatening condition for one to kick in, and there's no guarantee that it would.
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We may never know exactly what happens when we die, but many who have come close appear to be saying similar things about what they saw and heard.
Joe Harker