I have several large deer ferns. Some started to drop significantly during an unusually high summer drought in the Pacific Northwestern USA. I watered immediately and they did not perk up. They are still alive no doubt, but still haven't perked up after a dry fall. I wanted to relocate the ferns this fall and split them up. Do I have to wait now? What can I do to perk these guys up?
Transplanting is something best done if/when a plant is dormant; if that can't be achieved then done using a maximal amount of surrounding soil, so the roots (even the fine ones) are not cut.
In this case I would agree entirely with kevinsky - don't transplant, do water enough to keep the soil damp but not saturated.
It might be helpful (not sure) to ensure the plants are in at least dappled shade, to reduce transpiration.