This sounds like a case of gastritis, which means inflammation of the stomach. The stomach can become inflamed for a variety of reasons. I suspect that it happened in your case as a result of infection since you also mention that you had a temperature and were flushed. Such infection can occur with viruses and the illness tends to be of short duration. Gastritis can also happen as a result of eating contaminated food or even food that you are not accustomed to eating. Alcohol can also cause gastritis as can certain medications. You need not worry about the possibility of appendicitis because that condition would have progressed with increasing symptoms over the subsequent hours up to the point that you would have had no option other than seeking medical attention. Appendicitis progresses to a point of crisis and does not erupt and subside as your recent illness did. It is clear from your description that the illness has abated and no further action is required at this stage.