Since A Beautiful Mind opened, people who loved the movie but know that it is a fictionalized version of my 1998 biography of Nobel laureate John Nash have been asking me about the real Nash: How sick was he? How did he recover? How is he now?

A couple of weeks ago, Nash and I were at a cocktail party at the Institute for Advanced Study in Princeton. After regaling his listeners with box-office results, Nash joked that he hoped Universal was doing a better job of keeping its books than Enron. Watching this 73-year-old gentleman, you’d find it hard to believe that 15 years ago he was so sick that he was haunting the Princeton campus in mismatched plaids, speaking to no one, afraid to look anyone in the eye, his front teeth rotted.

In some ways, Nash’s illness was a classic case of paranoid schizophrenia. Some of his peers were convinced that the early stages of the illness manifested themselves in graduate school, but the full-blown symptoms did not erupt until he was 30. In 1959, just as he was about to be promoted to full professor at Massachusetts Institute of Technology, he told the chairman of a rival department that he wouldn’t be able to accept an offer because “I am scheduled to become the emperor of Antarctica.” Convinced that he was “a messianic figure of great but secret importance,” he frantically scanned The New York Times for encoded messages from aliens, and fiddled with radio dials to pick up signals from space.

At some point, he began hearing voices. Though he didn’t literally see the figures who were shouting at him, the voices were as real to him as people on the street. As a young mathematician, he saw mathematical solutions – nonrational flashes of intuition – long before he could work out the reasoning. After the delusions and hallucinations took over, he said, “My ideas about supernatural beings came to me the same way my mathematical ideas did. So I took them seriously.”

Nash responded dramatically to treatments available in the 1960s – crude and sometimes dangerous as these were. He was hospitalized half a dozen times, always involuntarily. At Trenton State, where he was incarcerated in 1961, he was injected with insulin and put into a coma daily for six weeks by physicians who hoped to shock Nash’s brain back to health. Later he was treated with antipsychotics such as Stelazine. He described the insulin shock as “torture,” and blamed Stelazine for making him “foggy” (both true).

Like so many people who suffer from schizophrenia, Nash did not believe that he was sick. As his illness deepened, he accused his wife, Alicia, of wanting to lock him away. Exhausted and depressed, struggling to raise their son, Alicia obtained a divorce in 1963. In 1965 he moved to Boston, where he hoped to begin his life afresh. But he stopped taking medication, relapsed and finally wound up living in Roanoke, Virginia, with his mother. At 40, gray-haired and frail, he saw “a cadaver almost” when he looked at himself in the mirror. He spent his days sipping Formosa oolong in his mother’s apartment.

Nash never stopped pining for Alicia, and she never really let him go. After his mother’s death in 1970, he wrote to Alicia and begged her to shelter him. Astonishingly, she agreed. He moved back to Princeton, where students knew him only as the Phantom of Fine Hall, a mute figure who scribbled weird but witty messages on blackboards: MAO TSE TUNG’S BAR MITZVAH WAS 13 YEARS, 13 MONTHS AND 13 DAYS AFTER BREZHNEV’S CIRCUMCISION.

Moviegoers will be surprised to learn that powerful new drugs such as clozapine played no role in Nash’s recovery. Another kind of chemistry apparently did, however. Like fewer than one in 10 individuals who suffer from chronic schizophrenia, Nash “emerged from irrational thinking ultimately without medicine other than the natural hormonal changes of aging,” as he later put it. No one knows why a lucky minority experience a dramatic lessening of symptoms in late middle age.

Even today Nash sometimes hears the old voices. But now he has learned to ignore them. “It’s like a continuous process rather than waking up from a dream,” he has said. Other Nobel laureates fly first class or start charities with their prize money. For Nash, who is doing research again, the most prized emoluments are simpler: being able to afford a cup of coffee at Starbucks, getting a driver’s licence and, most important, providing for his family – including a son who also suffers from schizophrenia – once more.

“A second take!” he quipped before kissing Alicia when they remarried last June. “Just like a movie.”