The 34-year-old made headlines around the globe when he battled a shark on live television while competing at a world tour event at Jeffreys Bay off South Africa's Eastern Cape province in mid-July.
About a week later, Fanning returned to the ocean off Australia's east coast to surf when he "saw a shadow go through a wave".
"I was like, 'You're kidding me' and I was like, 'Nah, nah, it's just a bird, it's just a bird'," the three-time world champion said from Tahiti, where he is set to compete in the next leg of the World Surf League Tour this weekend.
However, anxious to catch one more wave, Fanning stayed out on the water when he "saw a fin just come up and go through the wave".
"I was just like, 'Are you for real, what's going on here?'" he told the tour's organisers.
The surfer's return to the water was being filmed by an Australian television programme, and he admitted he agreed to take his board out at a spot he normally did not surf.
Despite his experiences, Fanning -- currently ranked second on the tour -- said he wanted to resume competitive surfing as soon as possible after the attack.
"If you leave it for too long, then your mind starts playing tricks on you," said Fanning.
"It makes the situation worse than what it actually is, and so, yeah, I just really wanted to get back out there."
Fanning said he was keen to put the South Africa attack behind him, telling Sydney's Daily Telegraph on Friday from Tahiti, "I'm very excited to be back in the water competing.
"It will be nice for people to start focusing on something different."
Fanning went on to add that he was more concerned about the conditions off Teahupo'o, which is renowned for its heavy waves.
"Over here it's pretty unlikely you're going to see any big great whites," the surfer, who won in Tahiti once in 2012, told the Australian Associated Press.
"I've been here many times. I'm comfortable with the wave, it's just a matter of surfing right at the right time."
Fanning told the Telegraph he had not sought professional help following the attack but would "talk it out" with his family and friends.
"It's not a taboo topic. I talk about it when I need to."