Lurking near her and the the huge mammal was a 15-foot tiger shark, Nan said, and though the animal is only visible in the distance in the footage, Nan's team also filmed the diver from aboard a nearby boat, capturing her coming to the surface and shouting that there was a shark nearby.
Out of shot, another whale was persistently tail slapping and keeping the shark away from Nan and the whale that was pushing her.
As Nan returned to the safety of the boat, in the waters off Muri Beach, Rarotonga, the Cook Islands, in October, the whale even surfaced to check on her.
Nan, who lives on the Cook Islands, said: 'I wasn't sure what the whale was up to when he approached me, and it didn't stop pushing me around for over 10 minutes. It seemed like hours. I was a bit bruised up.
'I've spent 28 years underwater with whales, and have never had a whale so tactile and so insistent on putting me on his head, or belly, or back, or, most of all, trying to tuck me under his huge pectoral fin.
'I tried to get away from him for fear that if he rammed me too hard, or hit me with his flippers or tail, that would break my bones and rupture my organs. If he held me under his pectoral fin, I would have drowned.'
She added: ‘I've spent the past 28 years protecting whales, and in the moment, I didn't even realize that they were protecting me!'