In 1988, when food rationing was a daily reality in communist Poland, railway worker Jan Grzebski fell into a coma after being hit by a train. Doctors gave him only two or three years to live but in June this year - 19 years after the accident - Grzebski awoke to find the communists had fallen from power.
'When I went into a coma, there was only tea and vinegar in the shops,' Grzebski told newspapers.
While waking from a coma after decades remains a rare phenomenon, patients such as Grzebski continue to stun the medical establishment and thrill their relatives.
A coma is usually caused by an injury to either side of the brain or to the upper brain stem. People may become comatose as a result of a range of conditions, including intoxication, brain injury, central nervous system diseases and acute neurological injuries such as stroke.
The Brain Injury Association of America defines a coma as 'a state of unconsciousness from which the individual cannot be awakened, in which the individual responds minimally or not at all to stimuli and initiates no voluntary activities'.
When people enter a coma they do not have sleep-wake cycles. They do not respond to pain or light but may move spontaneously. Most comas last for only a few days to a few weeks. Some patients will gradually regain consciousness and some will die, but others can remain in a vegetative state for years.