Seven days ago, Keizo Obuchi, the Japanese prime minister, suffered his stroke. It took most of last week for the surprise and panic to subside. It was no secret that Mr Obuchi had a pacemaker, but he didn't appear poorly and his last medical check-up showed no problems. At 62, in a country famous for the longevity of its citizens, he might have expected 20 more years of good health. But as the week wore on, a new question presented itself: not why Mr Obuchi fell ill so suddenly, but how he lasted so long.
The background to his illness came out in a press briefing which described in some detail Mr Obuchi's work regime. In his 20 months as prime minister, he took just three full days off. On weekdays and Saturdays he rose at 6am and started at the office at 8am - much earlier if there was a cabinet meeting. Work occupied him until 11pm, and he had fallen into the habit of waking himself up in the middle of the night to review paperwork and read reports.
He would sleep for only four or five hours, and even on Sundays there were visitors to receive and paperwork to catch up on. His last real holiday - two days of golf and relaxation in the mountain resort of Karuizawa - was eight months ago. In the week before his collapse, he had to deal with a volcanic eruption which displaced 15,000 people in the northern island of Hokkaido, and the defection from his government of a coalition partner. Then, eight days ago, he began to complain of dizziness. He was taken to hospital, where he fell into a coma from which he may never awake.
All prime ministers work hard, of course - Margaret Thatcher famously survived on five hours' sleep a night - and Mr Obuchi's case would not be so surprising if it was just the tragedy of one man in exceptional circumstances. In fact, he is just the most prominent among tens of thousands of Japanese who die, commit suicide or fall sick every year as a direct result of murderously long working hours. The situation has generated a word, which has been adopted for use in English by the UN's International Labour Organisation: karoshi, or death by overwork.
Such tragedies occur all over the world, of course, but not in the same way as in Japan. In Europe and America, victims of fatal work stress are typically at the top end of the scale - managers, executives and dealers whose responsibilities are matched by high rewards. "In Japan, both presidents and production-line workers die from stress," says Hiroshi Kawahito of the National Defence Council for Victims of Karoshi. "That indicates the seriousness of the problem."
No one knows precisely, but Mr Kawahito believes that at least 10,000 Japanese die from karoshi every year, not including those - like Mr Obuchi - whose lives are blighted by serious illness, disability or depression.
The most prominent case in recent years was that of Ichiro Oshima, a 24-year-old employee of Dentsu, the world's biggest advertising agency. Mr Oshima's career as a junior executive was even shorter than Mr Obuchi's tenure as prime minister and, from the account which his family's lawyers gave in court, he worked even harder. In his last month of life, he was regularly in the office until as late as 6am; he slept on average for between two hours and half an hour a night. In 1991, he became clinically depressed and killed himself. Last month, after seven years of legal arguments, the Supreme Court ruled that Dentsu was liable for the young man's death.
Japanese working hours are difficult to calculate because the official government figures derive from figures submitted by employers, who exclude unofficial and unpaid overtime. By this reckoning, average annual working hours have declined from 2,200 in 1988 to 1,980 in 1997 - comparable with Britain and the US. But surveys of workers themselves put the figure at 2,500 hours or, in industries like banking, 3,000 hours a year - the equivalent of 12 hours a day, five days a week.
What is it that makes the Japanese so tolerant of such demands? Partly, it is an ethic of hard work and endurance which begins in childhood with long hours of study for entrance examinations. Partly, it is the intense loyalty which many workers - although fewer than in the past - feel towards their companies. And Japan has few of the cultural institutions which help regulate working hours in other countries.
"In our culture, there are no internal factors that restrict us from working, there is no religious custom that prevents us from working on certain days," says Mr Kawahito. "Our whole society is controlled by a single value - greater efficiency, superior services and more competition."
The irony, of course, is that beyond a certain point, long hours diminish efficiency, over the short term and over a lifetime. The effects are felt, not only by the victims of overwork themselves, but by their families, friends and - in Mr Obuchi's case - the entire country. On the day he was inaugurated, the new prime minister Yoshiro Mori was mobbed by photographers outside his house, where he had just eaten breakfast with his young grandson. As Mr Mori observed, it may be a very long time before he is able to do that again.