If I have an amniotic sac condition will I need bed rest?

It depends. It depends on what the "amniotic sac condition" is. If it's something that is significant then it needs to be discussed with your ob/gyn and not over the internet.
Yes. Low amniotic fluid or if there is premature rupture of the sac causing a leak will often prompt the recommendation of bed rest. This helps your baby develop unless the situations deteriorates which may prompt delivery.