In a press conference aboard his jet as he returned from a trip to South Korea, Francis also mentioned the possibility of retiring from the Papacy if he felt he could no longer perform his duties.
His predecessor, Benedict XVI stepped down last year, an almost-unprecedented move that opened the way for Francis’s accession to the Papal throne.
‘I see it as the generosity of the people of God. I try to think of my sins, my mistakes, not to become proud. Because I know it will last only a short time,’ he said.
Then, apparently light-heartedly, he added: ‘Two or three years and then I’ll be off to the Father’s House.’
While the Pope has not spoken publicly before about when he might die, a Vatican source said he had previously told those close to him that he thought he only had a few years left.
Although the Francis is 77, he has been the most vigorous Pope in years, his energy proving the key to his popularity.
His frank admission may lead commentators to speculate as to whether he has any undisclosed health problems.
At the time of his elevation to the Papacy, reports emerged that Francis had a lung removed when he was a teenager in Argentina after suffering an infection.
Dr William Schaffner, chairman of preventive medicine at Vanderbilt University Medical Center in Nashville, Tennessee, said at the time: ‘Obviously, this was a success because here he is at age 76.
‘So whatever they did got him over that precarious period.’
As people age they generally become more susceptible to lung infections, such as pneumonia and bronchitis, according to the National Institutes of Health.
The risk increases if they have pre-existing conditions such as a weakened immune system or heart disease.
But today Francis only admitted that he had ‘some nerve problems’, which required treatment.
‘Must treat them well, these nerves, give them mate (an Argentine stimulant tea) every day,’ he joked.
‘One of these neuroses, is that I’m too much of a homebody,’ he added, recalling that the last time he’d taken a holiday outside of his native Argentina was ‘with the Jesuit community in 1975’.
Francis’s reference to ‘nerve problems’ may have been about his sciatica, which has been given as the reason Francis doesn’t bow before the Tabernacle when giving church services. In his first month as pope he hurt his sciatic nerve after using an uncomfortable chair.
Sciatica is the name given to any sort of pain that is caused by irritation or compression of the sciatic nerve, according to NHS Choices.
The sciatic nerve is the longest nerve in your body. It runs from the back of your pelvis, through your buttocks, and all the way down both legs, ending at your feet.
Resigning the papacy, as his predecessor Benedict XVI did last year, was also a possibility ‘even if it does not appeal to some theologians’, Francis told reporters.
He added that 60 years ago it was practically unheard of for Catholic bishops to retire, but nowadays it was common.