We eat a LOT of rice and have tried a lot of different things over the years. (Just starting to wonder if I need to be concerned about the news of lead and arsenic in rice....) Our preferred method is to soak white rice (which we rarely eat) for an hour, semi-polished rice (my favorite, from an Asian grocery store) for 12-24 hours and brown rice for 2-3 days. Yes, days!
In part the timing is at my convenience. In part it is weather-related: in warmer temperatures rice will start to ferment faster and doesn't need as long. If I start soaking rice and plans change I put it in the fridge until it's going to be cooked.
Also it *must* be rinsed after a long soaking. Daily in the case of a multi-day soak, otherwise just before cooking. Perhaps this was the problem with the 16-hour soaked rice that upset your stomach? After enough time and especially in warmer temperatures the water will turn yellowish or cloudy, there may be some bubbles or even scuzzy-looking stuff at the surface (especially if you forgot the change the water for two days - who me?)..... this is fine, just swish the rice in several changes of water until it runs clear and cook in fresh water or broth.
Which is also a key for us - we cook all our rice in homemade bone broth. I usually make enormous batches when we butcher an animal, reduce it down to a syrup, and freeze in little cubes. Then when it's time to make rice I just add a couple cubes to the pot.
For our family, we have come to appreciate the soaked and broth-cooked rice so much we can hardly stomach it any other way. And many of our friends have commented that our rice tastes better than any they have ever had! After soaking it cooks faster and is easier to chew (but not mushy) and digest. I hope this helps!