Monday was Sea Day in Japan, a public holiday when many people escape the summer heat by swimming, surfing and lounging at the beach. But not Prime Minister Sanae Takaichi.

Ms. Takaichi spent the holiday weekend rereading policy documents and dealing with a backlog of thousands of emails, according to a social media post on Tuesday. She wrote that she eked out a “full five hours of sleep for the first time in ages” — better than the “zero to three hours” she said she is accustomed to. And she said she spent her limited free time ironing undergarments, sewing fraying skirts and reinforcing loose jacket buttons.

With her comments, Ms. Takaichi seemed eager to present herself as a down-to-earth leader who doesn’t stop working on behalf of Japan’s citizens. Instead, her post, which has been viewed more than 31 million times, has set off a national debate about work-life balance and the hazards of sleep deprivation.

Toru Kunishige, an opposition lawmaker, warned that a prolonged lack of sleep “impairs judgment — much like a state of intoxication — and could pose a risk to national crisis management.”

Hiroyuki Konishi, another critic of Ms. Takaichi in Parliament, called for her resignation, saying, “The prime minister’s actual job is to set policy directions and issue instructions, not to pore over every last detail of a document.”

Yuichiro Tamaki, the leader of a populist conservative party, described Ms. Takaichi as hard-working but added that “resting is also a job.”

Ms. Takaichi’s office did not immediately respond to a request for comment.

Some commentators argued that Ms. Takaichi, the first woman to serve as prime minister in Japan, should be given more support in her position. While previous leaders often relied on their wives for help at home, Ms. Takaichi appeared to be tackling more domestic duties, according to Yoko Iwama, a professor at the National Graduate Institute for Policy Studies in Tokyo.

“Establishing a support system that allows a Japanese prime minister to focus entirely on their duties — without having to handle household chores personally — would contribute to women’s advancement in society,” Ms. Iwama wrote in the Nikkei, a prominent business newspaper.

Ms. Takaichi has been in overdrive recently to get her legislative priorities passed before Parliament breaks for the summer on Saturday. She is also grappling with continuing economic troubles — the yen has hit a 39-year low — and a recent dip in popularity, though her approval ratings remain relatively high.

In her post, Ms. Takaichi wrote at length about her recent workload. She said that since early July, “from early morning until late at night,” she had been holed up on weekends at her residence “poring over thick stacks of documents.”

She also shared personal details, saying she was “terrible at ironing and it takes forever.” But, she said, after her holiday ironing session, she “secured enough handkerchiefs and undergarments to last until the end of the session.”

“I can dive back in and give it my all starting tomorrow!” she wrote.

Ms. Takaichi’s allies have come to her defense, praising her for offering a candid view of the pressures of balancing work with personal commitments.

Ayano Kunimitsu, a vice foreign minister, said that Ms. Takaichi, like other politicians, faced pressure to manage chores on her own.

“Each person has their own circumstances and behind-the-scenes stories,” Ms. Kunimitsu wrote on X. “I would be grateful if you could understand.”

Japan has a reputation for long working hours, with days at some corporations exceeding 12 hours. In business and government, workers face pressure to stay at the office until superiors have left for the day and to log excessive amounts of overtime, which is seen as a sign of loyalty and diligence.

There have been high-profile cases in Japan in recent years of karoshi, or “death from overwork.” The issue came into the spotlight in 2016, when Matsuri Takahashi, an employee of Dentsu, the advertising giant, died by suicide after clocking more than 100 hours of overtime per month. Her death prompted the government to impose a limit of 45 hours of overtime per month, which some experts say has helped ease the work culture, especially for young people.

Since entering politics in the 1990s, Ms. Takaichi, who aspires to be a transformative leader, has made her work ethic a central part of her identity. Upon taking office as prime minister last year, she promised to “work, work, work, work and work.” She has skillfully deployed social media to highlight her busy schedule, writing a lengthy post in January about dealing with geopolitical issues while moving into the prime minister’s residence during the holiday season.

This is not the first time her habits have come under scrutiny. In November, she drew criticism for summoning her aides at 3 a.m. She later explained that her fax machine at home had broken, and she needed her staff’s help getting to another office so she could prepare for a meeting.