Thanks for all your concern, I was fine after arriving at the hospital.
I was told that it is
not just water, but minerals that I had lost too much for causing such symptom. I do aware of the heat, so I had been constantly drinking water (every 5mins) during the walk through a water tube . In those few hours( 9am to 2pm) , I drank 4 liters of water, 2 liters from home and 2 more from water filter near floating bridge entrance gate. The doctor advise me not just to bring water next time, but also sports drinks. Lesson learned.
Once again I would like to thank all for your concern and specially Ken's help (sorry to cause you lose your ride).
So to all bird watchers, please bring sports drinks!!
