The pathogenesis of ectopic gastric mucosa is a matter of debate between a congenital-embryological-and an acquired origin-consecutive to a gastroesophageal reflux (GER) like Barrett's esophagus -, the most commonly accepted theory being that these areas are embryological remnants.
Standard size latex filled helium balloons stay afloat for approx 8 - 12 hours, metallic helium filled balloons float for 2-5 days. I have found that a 36 latex helium filled balloon can stay afloat for a number of days due to the thickness of the balloon and the massive quantity of helium.
Like helium, you can fill balloons with xenon, but it is very expensive and the balloon becomes very heavy because the gas is so dense. An average balloon can hold around 40 lbs. (18.1 kilograms) of xenon, according to an experiment by the Royal Society of Chemistry. Xenon atoms added to liquid helium are used to observe quantum tornadoes.