In Japan, hikikomori, a term that’s also used to describe the young people who withdraw, is a word that everyone knows.

Tamaki Saito was a newly qualified psychiatrist when, in the early 1990s, he was struck by the number of parents who sought his help with children who had quit school and hidden themselves away for months and sometimes years at a time. These young people were often from middle-class families, they were almost always male, and the average age for their withdrawal was 15.

It might sound like straightforward teenage laziness. Why not stay in your room while your parents wait on you? But Saito says sufferers are paralysed by profound social fears.

“They are tormented in the mind,” he says. “They want to go out in the world, they want to make friends or lovers, but they can’t.”

Symptoms vary between patients. For some, violent outbursts alternate with infantile behaviour such as pawing at the mother’s body. Other patients might be obsessive, paranoid and depressed.