In countries like Vietnam and India where many people still get around on bicycle, visitors often find that cycling for all or part of their trip can offer the greatest opportunity to appreciate local life--the scents, sights and sounds that pass you by if you're whizzing through town in a taxi on the way to and from your hotel.
It is more likely that cycling combined with the dehydrating effects of a ten-hour plane trip plus a heat wave threw his electrolytes out of balance and triggered an event.