Your father is running a period of Shani Sadesatti. It is much stronger now as his Rashi is Dhanu / Sagittarius and Saturn is transiting through Sagittarius. The period till 2023 is not good, although period till January 2020 needs more attention. Ask him to do all his test properly. Sade satti period is going on so some chronic ailment will be there for which he will need medicine for a long time.