There are thousands of recorded examples of people having near-death experiences, with the most dramatic involving so-called "out-of-body experiences".

One of the most famous cases involved Pamela Reynolds, an American who had a rare operation in 1991 to remove a giant basilar artery aneurysm in her brain that threatened her life.

The size and location of the aneurysm meant it could not be safely removed using standard neurosurgical techniques.

She was referred to a surgeon who had pioneered a daring procedure known as "hypothermic cardiac arrest".

The operation, nicknamed "standstill" by the doctors who perform it, required that her body temperature be lowered to 60 degrees, her heartbeat and breathing stopped, her brainwaves flattened and the blood drained from her head.

In everyday terms, she was surgically killed and brought back to life.

During the time that Pam was in "standstill", she had a near-death experience. Her remarkably detailed out-of-body observations during her surgery were later verified to be very accurate.

This case is considered to be one of the strongest pieces of evidence in near-death experience research because of her ability to describe the unique surgical instruments and procedures used and her ability to describe in detail these events while she was clinically and brain-dead.

After witnessing the surgery on her own skull, she moved into a bright glowing light and met her deceased relatives before finally being restored to life.

Another famous case was came from a woman known simply as Maria. When she had a cardiac arrest in 1977, she floated out of her body, drifted round the hospital and noticed a tennis shoe on a window sill.

It was later found to be exactly where she said it was.

The shoe was said to be invisible from the ground and not in a location where Maria could have seen it.