yes, the external is terrible and burning; my ZSH (internal), can do it all - burn, stab, grab, sear - all depends on which nerve/where is being activated; can cause host of serious complications - I hope it is not this, but I had to google "no rash shingles" and take to my primary; even the i neurologist i saw had no clue (blank-face emoji if there is one) - and no repeat business. This can go wherever is a nerve - head to feet, all around skin & under, organs. Can stay dormant like the external, but once is in the internal nerves, can and will show up with no patterns, and without the rash, will never see it coming. At least my then-primary was interested; specialists where i knew more about me than they bothered/cared to learn - not at all. I put this out there as one of the too-many rare, uncommons that is not on anyone's radar - but is what we bring. Better to rule out then miss. Often the student must become the teacher. Wishing your father answers and relief.