Here is the ATSB summary with a link to the full report:
http://www.atsb.gov.au/publications/investigation_reports/2013/aair/ao-2013-047.aspx
While I have not read the entire report and cannot comment on the technical aspects (best left to those who work in aviation or who are scientists), is not a fair quick summary of this report 'whatever the consequences for one's employer, it is generally better to have a day off or go home if one genuinely is off colour, including when one has anything more than a slight headcold?'
Many of us know how colds affect us: we do not feel 'normal.'
(The report states that the Captain 'had a throat irritation that worsened as the day progressed....with further cold symptoms.' The crew had flown PER - SYD and on to MEL on A330 VH-EBV.) There were 11 crew and 211 passengers on board between SYD and MEL. It was probably the 1730 hours departure at the time in 2013.
In this circumstance if the Captain was away from his home city he could have either simply gone off sick and requested to travel as a passenger to his home airport or stay an extra night in an hotel and dose himself up with the usual remedies.
If no relieving staff were available this could have led to a flight (or more than one) being cancelled but the alleged outcome of the gent's sickness was not good. One would hope, however, that there were standby staff on call who with the usual couple of hours' notice could take on command of the particular flight(s) rostered for this staff member.
I am no physician but eating virtually nothing for a number of hours leads to one feeling poorly as blood sugar levels decline, does it not?