Emotions are felt in your gut. Feelings such sadness, anger, nervousness, fear and joy can be felt in the gut. Serotonin is well known as a brain neurotransmitter, yet a new study shows 90% of serotonin in the body is produced in the digestive tract. Some scientists even refer to serotonin as the “happiness chemical,” because higher serotonin levels increase feelings of well-being, confidence and belonging.