It is very kind of you to take the time to comment so fully and helpfully, and as you say the answer is not straightforward. The doctor wants me to have a full bladder at 10 a.m., but not to drink after 2 a.m. So I will take the minimum amount of water that will prevent dehydration and its effects.
Some months ago, I had a meal which upset my stomach for a couple of weeks. After the problem subsided, I was left with minor stomach pain, bloating, and gas in the upper abdomen so that I was burping throughout the day.
I went to Prachuap Khiri Khan Hospital and to the center on the third floor where people pay one or two thousand baht for a check-up. The doctor prescribed Omeprazole and Domperidone tablets and a couple of bottles of Alum Gel. After three weeks, I felt fine, but in view of my age, the doctor advised me to have the ultrasound test. Out of my hearing, she told my wife that she wanted to check the condition of my aorta.
The woman doctor, by the way, was very thorough and really good - this is for those who might live in Prachuap.