I almost always use the bivvy bag over my sleeping bag during the colder periods. Firstly my bag lets wind through!! and gets very cold and also for the dampness in the air that cling to the bag normally on misty mornings. It also allows me to take a smaller tarp without the concern of getting (to) wet.
Getting in is easy sit in the middle of the hammock put you feet in swing around then do the caterpillar dance to shuffle up the bag over your shoulders.
I don't normally bivvy bag up to above the chest area .. Getting out is similar only opposite way around. Taking a pee bottle helps saves getting out in the middle of the night and avoids a middle of the night caterpillar dance
Getting in is easy sit in the middle of the hammock put you feet in swing around then do the caterpillar dance to shuffle up the bag over your shoulders.
I don't normally bivvy bag up to above the chest area .. Getting out is similar only opposite way around. Taking a pee bottle helps saves getting out in the middle of the night and avoids a middle of the night caterpillar dance