The story of how <a href="https://www.thenational.ae/uae/health/emirati-woman-wakes-up-from-coma-after-almost-30-years-1.851923">Munira Abdulla spontaneously woke from a coma after 27 years </a>has shed light on how someone could come back to life after decades of unconsciousness. Her case is by no means the first, though it is remarkable given the period of time that has passed. The coma itself - a state of unconsciousness - occurs after a severe head injury or stroke, though can be a result of severe poisoning or a brain infection. Patients with diabetes can also fall into a coma if their blood glucose gets out of control. Most comas do not last for more than two to four weeks. A patient’s potential for recovery often relates to their score on what's known as the Glasgow Coma Scale tool, which assesses three areas: eye opening, verbal response to a command and voluntary movements. A score of one means no eye opening, while four means the patient is able to open their eyes spontaneously. Doctors say patients who score three to four in the first 24 hours of falling in a coma are likely to either die or remain in a vegetative state. It is not always clear why some patients spontaneously wake, although doctors are seeing some success in using medication. Amantidine, a drug to treat Parkinson’s has shown promise, as has zolpidem, a sleeping aid. As past cases have shown, patients often find themselves in a very different world. Family members may have passed away and loved ones moved on to new relationships. The most notable cases include: The American, from the Ozark mountains, fell into a coma after suffering a serious head injury in a road accident in 1984. He was initially diagnosed as being in a persistent vegetative state, but gradually became minimally conscious, meaning he was occasionally responsive. On June 11, 2003, he said his first word, 'mum,' 19 years after he last spoke. Doctors studied his brain, showing how it was able to grow new connections, effectively rewiring itself after almost two decades. His personal circumstances shed light on the world coma survivors can be themselves returning to. Wallis would not have known that the 17-year-old bride he kissed goodbye on the night of his accident would go on to have three children with another man. And he had to come to terms with the fact that Amber, the six-month-old daughter he left behind, was a 20-year-old strip club dancer when he woke. An American millionaire heiress and socialite. Her marriage to her husband Claus had been difficult, and he was suspected of injuring her, causing her to fall into a coma in 1979. She recovered, only to enter a second coma a year later in 1980. Her husband, who stood to inherit her fortune, was twice found guilty in the 1980s of attempting to murder her by injecting her with sedatives and insulin, but was later acquitted on appeal. She did not wake from the second coma, dying 27 years, 11 months and 15 days later of a heart attack in a New York nursing home. Esposito holds the record for the world’s longest coma. She went in for a routine operation, the removal of her appendix, as a six-year-old on August 6, 1941. But she never woke from the general anaesthetic, staying in a coma for 37 years and 111 days, before dying in 1978. Dubbed 'sleeping beauty' by the press, she survived numerous operations while comatose, including pneumonia and measles. Her family even took her to the grotto at Lourdes in France, hoping for a miracle. A US police officer, he was shot in the head while responding to a call in Tennessee in 1988. He fell into a coma, which he remained in for eight years, but spontaneously woke in 1996 after undergoing lung surgery. He began talking non-stop and was able to remember the names of friends and relatives, his horses and the colour of his car. But it did not last long. He fell into a coma again 18 hours later and died the following April, at the age of 43. The F1 star was placed in a medically-induced coma after suffering a serious brain injury while skiing in the French Alps in December 2013. Schumacher, a seven-time world racing champion, has never been seen publicly since. Since his release from hospital he has been treated at his home in Switzerland, reportedly at a cost of tens of millions of dollars. It is not clear whether he remains unconscious and his family, frustrated by tabloid media intrusion, issue few updates. But sources have told media he is no longer bed-ridden nor existing on tubes. His family said they celebrated his 50th birthday in January this year. "You can be sure that he is in the very best of hands," a statement said at the time. The South African fell into a coma after being severely injured in a car accident in Eastern Cape in 2005. His doctors agreed to treat him seven years later with a sleeping pill after being persuaded by his wife, who had conducted research into the topic. He regained consciousness after five days of treatment. The case caused a sensation and South African media dubbed the simple pills, Stilnox, the 'Lazarus drug'. Another South African, Louis Viljoen, 24, was given the same treatment in 1999, five years after he was hit by a lorry and left in a coma. He awoke 25 minutes later, though medics have cautioned that the treatment is unproven.