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.
Latex balloons will last about a day to a day and a half at best, unless treated with what the balloon industry calls Hi Float, which is a rubbery coating applied to the inside of a latex balloon prior to inflating. Then it will last for days as it slows the seep of helium through the balloon membrane.