That deep sleep is a demonic force...you were doing a lot of good.
I am not a person who sees the devil in every detail, but this is a known trick, just like Peter and John who fell asleep when Jesus asked them to pray.
Corrie Ten Boom noticed the tired feelings as a demonic force that she had to cast out.
Cast it out and continue to pray!
Or it could have been the Lord saying, "Rest."
Nope, I saw the deep sleep as something God gave to refresh me. He knows I needed it. I had finished praying before I feel asleep. And I woke up ready to pray even more.