As pilot I was required to have a Medical every six months and one of these every two years had to be at C.M.B. Doctors told me of one pilot who had passed his Medical in the morning - and then dropped dead in the street in afternoon. ( The unpredictable - as has been mentioned by others.)
"Six monthly flying checks" do not appear to have been done, until I had completed some 3500 hours with two different U.K. employers and different aircraft types, mainly Trooping worldwide, as the only other pilot, on board ( just a C.P.L. with I/R were enough, even to operate some B.O.A.C. First Class services.) Standards as well as passenger capacities and speeds have altered since !
LT