Kay Longstaff, 46, says she was sitting on the deck of the Norwegian Star cruise ship when she fell into the water shortly before midnight on Saturday.
She was found alive the next morning, floating some 95 kilometres off the coast of Croatia.
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“I am very lucky to be alive,” she told the Croatian news channel HRT on Sunday.
Longstaff stayed awake by singing to herself, according to Lovro Oreskovic, the captain of the Croatian rescue ship that found her.
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“Luckily for her, we saw her immediately because she raised and waved her hands when she saw us,” he told The Associated Press.
Longstaff was later taken to the town of Pula to be treated in hospital.
— With files from The Associated Press