Can anyone describe to me how a baby falls asleep in a back carrier like an ergo?

[mumtocuddlebundle]

I am interested in what happens. And the logistics of supporting their head while sleeping.
When they fall asleep their head must go all floppy. Do you notice the head lolling around behind you? Then attach hood for support? Or do you attach hood in anticipation of them falling asleep? Or do they tend to rest their heads on your back as they go to sleep?
Can anyone shed any light? Thanks very much.

I have an Ergo - DS tends to flop forward onto my back. Otherwise yes his head lolls to an extent... I kind of let it take care of itself. It's akin to what it's put through in the buggy (Phil & Ted extra seat with no sides).

Thanks