[wkat4242]

True, it's not ideal.

I wonder though if there were similar complaints when the flight engineers were phased out, which obviously worked out fine (things are actually a lot safer back then).

For example they could do things like pee tubes (With M/F suitable private receptacles) which some private jets have in the cockpit. So it's not necessary to wake up the other pilot all the time. But yeah a long bumpy flight would be exhausting for both.