A 28-year-old male is referred to psychiatry by his gastroenterologist after an extensive negative medical workup for chronic regurgitation. He reports that for the past 10 months, he has been repeatedly regurgitating partially digested food within 15 to 30 minutes after eating most meals. He describes the regurgitation as effortless and not preceded by nausea, retching, or disgust. He sometimes re-chews and re-swallows the food and other times spits it out. The behavior occurs involuntarily though he acknowledges he can sometimes suppress it in social situations with significant effort. He has lost 12 pounds over the past year due to food avoidance at social meals and has become increasingly isolated. His gastroenterology workup including upper endoscopy, esophageal manometry, gastric emptying study, and pH monitoring has been unremarkable. He denies self-induced vomiting, body image distortion, fear of weight gain, or binge eating. What is the MOST likely diagnosis?