“When I pray, sometimes I fall asleep,” he said in an episode of a Catholic TV2000 television programme published on Youtube.
“Saint Therese used to do it too”, the 80-year-old pontiff said – in reference to the 19th Century Catholic saint.
But he said that falling asleep during prayer actually pleased God and that Christians were called to “feel like children lying in their fathers’ arms”.
Reports say that the pontiff usually goes to sleep at about 21:00 local time (20:00 GMT), but wakes up at around 04:00 (03:00 GMT) every morning.
The Argentine has been head of the Roman Catholic Church since 2013, and has a busy schedule of international visits and public appearances.
He has become known for some moderate reforms and openness in his papacy – in particular his use of simple, direct language.