Boris Johnson reveals doctors prepared to announce his death during coronavirus battle
The Prime Minister spent three nights in intensive care at St Thomas' in London with the disease, where he said medics gave him "litres and litres of oxygen".
He described it as a "tough old moment", telling the Sun On Sunday: "They had a strategy to deal with a 'death of Stalin'-type scenario.
"I was not in particularly brilliant shape and I was aware there were contingency plans in place.
"The doctors had all sorts of arrangements for what to do if things went badly wrong.
"They gave me a face mask so I got litres and litres of oxygen and for a long time I had that and the little nose jobbie."
Mr Johnson, 55, said it was "hard to believe" his health had deteriorated in just a few days, saying he "couldn't understand why I wasn't getting better".
The PM told the paper the "indicators kept going in the wrong direction" and that he kept asking himself: "How am I going to get out of this?"
"The bad moment came when it was 50-50 whether they were going to have to put a tube down my windpipe.
"That was when it got a bit ... they were starting to think about how to handle it presentationally."
He said he was "in denial" initially about how serious his illness was, and that doctors were right to "force" him to go to hospital.
After a fortnight convalescing from the virus, and just two days after he returned to work full-time, his fiancee Carrie Symonds gave birth to their son, Wilfred Lawrie Nicholas Johnson.
They named him after their grandfathers, and two doctors - Dr Nick Price and Prof Nick Hart - who helped save Mr Johnson's life.
He shared his experience of the disease as the number of people who have died in hospitals, care homes and the wider community after testing positive for Covid-19 in the UK as of 5pm on Friday rose to 28,131, up by 621.
The death toll has edged closer to that of Italy, which now stands at 28,710 and is the highest in Europe, according to data from Johns Hopkins University.
And the number of daily tests both concluded and sent out in the last 24 hours dropped to 105,937 from 122,347 the previous day.
Of those, the number of people tested also fell - down to 63,667.
It comes as questions were raised over how tests are being counted after Health Secretary Matt Hancock said on Friday he had met his target for 100,000 Covid-19 tests per day.