Question

y does nausea occur and y does acidity occur after eating something bitter

Answer 1

I believe your referring to the GERD. Gastroesophageal reflux disease (GERD) is a condition in which the stomach contents (food or liquid) leak backwards from the stomach into the esophagus (the tube from the mouth to the stomach). This action can irritate the esophagus, causing heartburn and other symptoms.
http://www.nlm.nih.gov/medlineplus/ency/article/000265.htm