First off, you generally want to look at placements of planets like Mercury, the Moon and Saturn, just to start. House placements, not just signs, are important. Mercury would cover things like your general thought processes and relational ability, and the extension of this could be expressed by positions of signs like Gemini and Virgo, but also detriments and such. As to nerves in a physical sense, the Moon generally governs the body, so her aspects are important. Saturn rules over "melancholy", which in an ancient sense can cover a whole range of "distempers" to include bad nerves. In addition, you can get combinations of placements and aspects that produce similar effects as what may seem more obvious in a chart. It can all get pretty complicated.
In terms of a medieval perspective though, the medical astrology of the day wouldn't be much interested in a person's mental health. It's not that it wasn't considered and issue is that its more of a job for a parish priest, as mental suffering was considered a moral disorder. The medieval doctor was more of a university trained philosopher than what we would now call a doctor, relying on his reading of Galen, Aristotle and Hippocarates without much concern for doing actual physical medicine. In fact, he didn't even want to see his patients as this was below his status. He would just have the patient, through an intermediary servant, drop of a sample of their urine and then study it in the light to see its color and viscosity. He would also do a birth chart , match it to the current heavenly positons, jot off a diagnosis and collect a hefty fee. Typical physical ailments would result in sending the patient off to the pharmacist to buy a potion that you
should pray to God would not kill you. If it was a physical ailment that involved surgery, the doctor would send the patient to a "physician" who could just as easily be a butcher. Mental ailments, such as bad nerves, might get a recommendation to go to a priest and confess.
My reference for the above perspective is
The Devils Doctor: Paracelsus and the World of Renaissance Magic and Science by Phillip Ball. The author covers a lot of background in terms of Medieval medicine and astrology, and it made me thankful for our modern conveniences.
I also watched this video recently and it gave me some food for thought. The focus is more on combat related PTSD, but medieval life had plenty of room for about every kind of stress. "Moral injury" is an interesting concept.
