PARIS, France - Emerging from an extended, drug-induced coma such as that into which Michael Schumacher was placed after a skiing fall could take several days - or, tragically, not happen at all.Doctors on January 30 2012 started the slow business of bringing the Formula 1 legend out of an artificial deep sleep into which he was placed after a near-fatal skiing fall in December 2013Gerard Audibert, a neurosurgeon at the University Hospital in Nancy, eastern France, explained: "After a progressive reduction of the sedative it can take several more days for the last traces of the drug to disappear from a patient's system. There is a grey zone (between awake and sleep) that lasts several days but it varies from one patient to another."Awakening was not guaranteed.'MOVES A BIT'"The patient may well stay in a coma," Audibert warned, and Parisian anaesthesiologist Bernard Vigue added that when it did happen the wakening was always "visible"."The patient opens his eyes or moves a bit."The coma was induced to let Schumacher's brain rest and to reduce pressure inside the skull caused by bruising and bleeding. The coma would be eased when pressure stabilised and he was able to breathe without the needed ventilator.Vigue said Schumacher could have months, if not years, of therapy ahead of him. "Recovery can be a very long road. In some cases, patients improve between a year and three years later."Schumacher hit his head on a rock when he fell while skiing in the French Alps.