Health/fitness is a funny thing - I know someone who is probably the healthiest person I know, never smoked, never drank, very disciplined diet, regularly runs, swims and rows and competitive sports, etc. and so on - had a stroke/heart attack at less than 40 (survived), the doctors reckon (long term) dehydration was a major factor - despite a reasonable fluid intake it was probably insufficient for their specific needs.
Though thinking about it while posting I wonder with the timing whether COVID was in any way involved.