BRAINTREE, Mass. — A 53-year-old Massachusetts hospital worker stepped forward Thursday to claim the biggest undivided lottery jackpot in U.S. history — $758.7 million — after breaking the news to her employer the way the rest of us only dream of: “I called and told them I will not be coming back.”

“The first thing I want to do is just sit back and relax,” Mavis L. Wanczyk told reporters at a news conference.

Wanczyk chose to take a lump-sum payment of $480 million, or $336 million after taxes, lottery officials said. Winners who take a gradual payout stand to get more money spread out over several decades.

The previous evening, she recalled, she was leaving work with a firefighter and remarked, “It’s never going to be me. It’s just a pipe dream that I’ve always had.”