A stomach upset is a very common symptom but identifying its exact cause becomes difficult as most gastrointestinal problems cause stomach upsets. However, other symptoms present along with the stomach upset could help in determining the root cause. If you're suffering from a stomach upset then you're most likely to be diagnosed with one of these problems. 1. Anxiety: If your stomach started grumbling right after getting caught up in a stressful situation, it’s clearly due to anxiety. Under stressful situations, physiological and endocrine changes that take place can cause digestive distress and give rise to symptoms like stomach cramps, diarrhea