Mark,
Fainting after a meal is probably more common than you think (but not the norm of course); your body diverts blood to digest the meal, sometimes causing a shortage elsewhere, this can (and almost certainly will) be exacarbated by alcohol.
However, the indigestion you mention is worrying in that it could be indicative of a cardiac event causing hypotension.
Definitely worth running it past the gp, however long ago it was.
Can't see it being CO2 poisoning, with only one pax symptomatic out of a few hundred...
All the best.