Is it distressing to experience consciousness slipping away or something people can accept with equanimity? Are there any surprises in store as our existence draws to a close? These are questions that have plagued philosophers and scientists for centuries, and chances are you've pondered them too occasionally.

None of us can know the answers for sure until our own time comes, but the few individuals who have their brush with death interrupted by a last-minute reprieve can offer some intriguing insights. Advances in medical science, too, have led to a better understanding of what goes on as the body gives up the ghost.

Death comes in many guises, but one way or another it is usually a lack of oxygen to the brain that delivers the coup de grâce. Whether as a result of a heart attack, drowning or suffocation, for example, people ultimately die because their neurons are deprived of oxygen, leading to cessation of electrical activity in the brain - the modern definition of biological death.

If the flow of freshly oxygenated blood to the brain is stopped, through whatever mechanism, people tend to have about 10 seconds before losing consciousness. They may take many more minutes to die, though, with the exact mode of death affecting the subtleties of the final experience. If you can take the grisly details, read on for a brief guide to the many and varied ways death can suddenly strike...