As it turned out I spent 2 days with suffering from stomach cramps that felt like being disemboweled (plus a good deal of other unpleasantness I won't go into). The beginning of relief only came when we made it back to town and Mel came back from the pharmacy with antibacterial medication and a sachet drink that tasted a bit like liquid clay. Then my neck started siezing up and I was so dizzy I could hardly leave the hotel room for another 2 days.
After more visits to the pharmacy and some internet research we discovered that the new symptoms we're listed under serious side-effects of the medication I was taking. All told it was a good 5 or 6 days before I returned to somewhere like normal (for me anyhow).In the end I was just glad it happened where it did and we had the time to deal with it. We still had plenty of time to do loads of great things like riding (and feeding) elephants, white water kyaking (kind of scary), taking a slow boat up the Mekong or visiting the picture postcard perfect Khang Si waterfall.