The 55-year-old Briton, who underwent surgery in August, told the Times newspaper on Friday that it had changed his perspective on life even if his will to win remained as strong as ever.
"There's bound to be fear. It's the great unknown," he said of undergoing a five-hour operation three weeks ago.
”I think I’m resilient, tough. I can put up with a lot but in hospital one day I was overwhelmed if I’m being honest.”
Brailsford said he had suffered bouts of chronic tiredness "like someone taking my battery out" before the diagnosis, but had blamed travel fatigue.
Going for a scan, he was still focused more on the Tour, with Britain's richest man Jim Ratcliffe taking over funding of the highly successful Team Sky and transforming it into Ineos.
The scan showed a tumour: "My attitude had been ridiculous, really, looking back," said Brailsford. "That was the first time I was stopped in my tracks."
Then watching Ineos rider Egan Bernal become the first Colombian to win the Tour was particularly emotional "because I am thinking 'who knows, I might not do this again'."
Brailsford, who has taken Bradley Wiggins, Chris Froome and Bernal to Tour glory, said he tried to hurry back until he received a text telling him it was not a test of personality and he needed time to heal.
“I needed to hear it because it's the opposite of how I usually am," he said. "I would think 'if I try harder I'll get back quicker'."
Brailsford said it had been 'liberating in one way' to be forced to slow down and appreciate simple things like going for a walk.
"Froomey was telling me there was a point when he could get out of bed into a wheelchair and go to the loo by himself. For him that was monumental," he said. "We have been chatting about when I can fly down and we can convalesce together."
Froome missed the Tour after a crash at the Criterium du Dauphine put him in intensive care.