He talked about this in an interview a few days ago.
Aleteia posted details on Tuesday:
“When I pray, sometimes I fall asleep,” Pope Francis confessed during the second episode of the Padre Nostro (“Our Father”) television program on the Italian Catholic television station TV2000, in an excerpt published on YouTube today.
“St. Thérèse of the Child Jesus did that too,” the pope recalled.
Hey, it happens to me, too. I often get lulled to sleep praying the rosary. Luckily, I usually do it with my wife, who nudges me awake when I start to snore…