bad gas

hypochondria (n.)
1839, "illness without a specific cause," earlier (1660s) "depression or melancholy without real cause," earlier still (late 14c.) ipocondrie "upper abdomen," from Late Latin hypochondria "the abdomen," from Greek hypokhondria (neuter plural of hypokhondrios), from hypo- "under" + khondros "cartilage". Reflecting ancient belief that the viscera of the hypochondria were the seat of melancholy and the source of the vapors that caused such feelings.