Not a pilot, so of course I don't know the kind of pressure in the cabin, but I would've guess it was normal?
Like I wouldn't exxpect someone to be 100% vigilant 100% of the time, especially in long duration flights. That's why there's two pilots, if you are ona clear sky, no turbulence, perfectly calm conditions, I wouldn't see much of a differrnce in them relaxing and chatting over coffee or just a 15 minutes power nap (not on 1 and a half hours long journey of course)
Yeah, a hearth attack is an extreme case, but tiredness would be a pretty likely and frequent cause of incapacitation in my opinion.