The reason Rommie isn't shown for much for the fifth Season was due to Lexa Doig's real life pregnancy. If you look closely you'll notice that when she is on screen she's either shown from the neck up as Andromeda, or from the back. She wasn't seen full front view until episode 5.18.
The title Quantum Tractate Delirium literally translates to: "the minimum amount of any physical entity involved in an interaction in physics" "signifies a treatise" "severe neuropsychiatric syndrome". This describes Rommie's mental state and physical damage.
On two occasions Harper fears that hitting Rhode will burst his " epidermal sac". There are the radial and ulnar bursal sacs extending from the wrist into the hand, but there is no such thing as an epidermal sac. Although "epidermal" does mean of or pertaining to the skin and you can split your skin by hitting something very hard.