Cruise Flu, norovirus I think is the proper term, is very unpleasant.
It happened to me on a Disney cruise while with family on New Years Eve. Being sick to your stomach or diarrhea every 10 or so minutes for 8 hours , followed by being confined to your room for two days because of it isn't fun for you or your wife.
Then my wife was sick the morning we got off. There is a shot that stops it if you get it soon enough, my wife did. She was a miserable zombie getting home.
This could be your excuse.
