For Shakespeare, death was 'that undiscovered country' from which 'no traveller returns'. But today, as medical science improves, more and more patients can almost literally be brought back from the dead. And occasionally they tell of strange experiences, some of which appear to defy scientific explanation. Dr Peter Fenwick, an expert in brain function, has made a special study of 'near death experiences'. He asks: are they simply hallucinations; true glimpses of an afterlife; or do they hint at a new dimension of human consciousness?