Thirty-year-old Hiroko Sato was having her hair done, just as she had every month for the past several years, when suddenly she began to feel ill. First, she felt dizzy, then nauseous, then her hands started to go numb. She tried to shrug it off, but when she rose from her chair, she fainted.

The next thing she knew, she was in hospital, her symptoms now including shortness of breath and heart palpitations. A tranquilizer drip offered relief, so much so that the next day Sato was able to round up her baby and small child to make the planned move to the Tokyo home where she started living with her husband's parents.

But her recovery didn't last. A week later, Sato (not her real name) suffered a similar experience and, from that day on, began having difficulty performing the most routine tasks. It got so bad that going shopping, driving, taking the train and even staying home alone became almost out of the question for fear of another attack.