It could be a couple of things George
It could be they are about to pass a soft shelled egg, although strange for two to do it at the same time
These eggs really seem to drain chickens but once they are passed then they perk back up
Do they have access to oyster shell and grit?
Other thing is check their crops first thing in the morning they should feel empty
Do they free range or are they in a run? What type of bedding material do you use in the nest boxes?
Reasons I ask long grass and hay can cause crop problems
Sarah