Sciatica as pinto outlined often causes pain remote to the area of insult. It is very hard to offer specifics however, groin pain can be caused by nerve disruption as well as musculoskelatal reasons. It can also be referred from problems elsewhere. Opioid pain relief(morphine based) can often affect respiratory drive so must be used wisely in those at risk of breathing problems. People may also become acutely confused from urinary tract infections, moreso the elderly.
Not meant to be advice, hope your dad is up and about soon.
